Tetrapod trackways from early Middle Devonian pose interesting questions
pnyikos
about what appear to be tetrapod trackways that predate such well-
known tranisitional fish fossils as those we have of Eusthenopteron,
Panderichthys, and Tiktaalik:
http://www.nature.com/nature/journal/v463/n7277/full/463040a.html
http://www.nature.com/nature/journal/v463/n7277/full/nature08623.html
http://www.nature.com/nature/journal/v463/n7277/covers/
You may need to pay for these, so here are two popularizations
available for free:
http://www.cbc.ca/news/technology/story/2010/01/06/science-fossil-four-footed-animals.html
linked from:
http://dinosaurs.about.com/b/2010/01/07/the-400-million-year-old-tetrapod.htm
The favored explanation for the discrepancy, reminiscent of the
similarly big gap for the first birds vs Dromaesaurs, is that
Eusthenopteron, Panderichthys, and Tiktaalik are "relicts" from an
earlier era where very similar transitional forms exist.
But I can think of several others, and my interpretation of the
trackways is not adequate to settle the first one:
1. These tracks represent a parallel evolution of a "failed
experiment" in tetrapody.
2. The "tracks" are natural geological formations, like the
"footprint" of "Thinopus".
3. The trackway has been improperly dated.
Can anyone help decide between the above four possibilities, or argue
for yet others? "possibility zero" is the favored explanation I gave
above.
Peter Nyikos
Professor, Dept. of Mathematics -- standard disclaimer--
University of South Carolina
http://www.math.sc.edu/~nyikos/
nyikos @ math.sc.edu
Arkalen
> In the 7 January 2010 issue of _Nature_, there is a pair of articles
> about what appear to be tetrapod trackways that predate such well-
> known tranisitional fish fossils as those we have of Eusthenopteron,
> Panderichthys, and Tiktaalik:
>
> http://www.nature.com/nature/journal/v463/n7277/full/463040a.html
> http://www.nature.com/nature/journal/v463/n7277/full/nature08623.html
> http://www.nature.com/nature/journal/v463/n7277/covers/
>
> You may need to pay for these, so here are two popularizations
> available for free:
>
> http://www.cbc.ca/news/technology/story/2010/01/06/science-fossil-four-footed-animals.html
> linked from:
> http://dinosaurs.about.com/b/2010/01/07/the-400-million-year-old-tetrapod.htm
>
> The favored explanation for the discrepancy, reminiscent of the
> similarly big gap for the first birds vs Dromaesaurs, is that
> Eusthenopteron, Panderichthys, and Tiktaalik are "relicts" from an
> earlier era where very similar transitional forms exist.
>
> But I can think of several others, and my interpretation of the
> trackways is not adequate to settle the first one:
>
> 1. These tracks represent a parallel evolution of a "failed
> experiment" in tetrapody.
What do you mean by that ? At all times species contain many many
individuals and many many related species coexist, only one of which can
be the common ancestor of any future group, so it's obvious that
tetrapody involved a whole lot of "failed experiments", i.e. some
members of the proto-tetrapod group that remained proto-tetrapods until
they went extinct and didn't spawn the actual tetrapods, or spawned
close cousins that went extinct. That's the same thing as saying that
Tiktaalik et al are "relics" from an earlier era.
If by "parallel evolution" you actually mean other groups completely
unrelated to the group that spawned tetrapods evolving into
tetrapod-like creatures and disappearing, well, it's possible, but
there's no evidence for it. More than that, given in this case we're
hypothesising an *earlier* parallel group (in fact it's specifically to
explain why these tracks are so early that you're suggesting a parallel
group) I'd expect the opposite to happen. If a group starts exploiting a
new niche and is successful at it (say, successful enough that they
leave evidence in the form of fossil tracks) they'll tend to radiate and
occupy the niche and make it more difficult for other groups to evolve
the same way later.
>
> 2. The "tracks" are natural geological formations, like the
> "footprint" of "Thinopus".
>
> 3. The trackway has been improperly dated.
>
> Can anyone help decide between the above four possibilities, or argue
> for yet others? "possibility zero" is the favored explanation I gave
> above.
Possibilities 2 and 3 are for professionals to judge; as far as I know
the tracks and their date are accepted as genuine so while this may turn
out to be false, possibilities 0 and 1 are plausible enough that I can
provisionally reject 2 and 3. I think 0 makes the most sense. Do you
have a specific objection to it ?
John Harshman
All are conceivable explanations, though 2 and 3 seem unlikely unless
you have some argument for either of them. 0 seems best. Do you have a
preference?
pnyikos
> pnyikos wrote:
> > In the 7 January 2010 issue of _Nature_, there is a pair of articles
> > about what appear to be tetrapod trackways that predate such well-
> > known tranisitional fish fossils as those we have of Eusthenopteron,
> > Panderichthys, and Tiktaalik:
>
> >http://www.nature.com/nature/journal/v463/n7277/full/463040a.html
> >http://www.nature.com/nature/journal/v463/n7277/full/nature08623.html
To get the really detailed photographs you need to get the pdf version
of this second _Nature_ reference. Online it is even better than the
online "full" version that is directly accessed above if you have
online access. I have it at my university, but not at home.
If the "full" version is what actually appears in the printed journal,
that is second best. Or maybe third best--I didn't bother to access
the supplemental information at work, also available online thru my
university account.
> >http://www.nature.com/nature/journal/v463/n7277/covers/
>
> > You may need to pay for these, so here are two popularizations
> > available for free:
>
> >http://www.cbc.ca/news/technology/story/2010/01/06/science-fossil-four-footed-animals.html
This one features one photograph and some good discussion, but the pdf
version of the second _Nature_ has really good enlargements, some of
which aren't of tracks in the one photograph this cbc news item
provides.
> > linked from:
> >http://dinosaurs.about.com/b/2010/01/07/the-400-million-year-old-tetr...
This one is just an announcement, and the abstracts of the two
_Nature_ articles [which is what you get by clicking if you don't
subscribe to full access] already do a better job.
> > The favored explanation for the discrepancy, reminiscent of the
> > similarly big gap for the first birds vs Dromaesaurs, is that
> > Eusthenopteron, Panderichthys, and Tiktaalik are "relicts" from an
> > earlier era where very similar transitional forms exist.
>
> > But I can think of several others, and my interpretation of the
> > trackways is not adequate to settle the first one:
>
> > 1. These tracks represent a parallel evolution of a "failed
> > experiment" in tetrapody.
>
> > 2. The "tracks" are natural geological formations, like the
> > "footprint" of "Thinopus".
>
> > 3. The trackway has been improperly dated.
>
> > Can anyone help decide between the above four possibilities, or argue
> > for yet others? "possibility zero" is the favored explanation I gave
> > above.
>
> All are conceivable explanations, though 2 and 3 seem unlikely unless
> you have some argument for either of them.
And I don't. The second article does what looks like a good job of
taking care of 3, and its case for 2. being false looks convincing.
>0 seems best. Do you have a
> preference?
Mine is for 0 also, though 1. is an intriguing possibility.
Have you looked at the enlarged photos of the prints? They seem
compatible with 1. despite the following claim by the authors of the
first _Nature_ "article" [it comes under "News and Views", not
"Articles"], which seems rather subjective to me:
The match between these tracks and the limb
anatomy of *Ichthyostega* and *Acanthostega*
is impressively close: were similar tracks to be
found in Famennnian/Frasnian rocks, they would
be readily attributed to an *Ichthyostega*-like
animal, as were the reviously reported late
Devonian trackways (Fig. 1.)
--p. 41, starting column 2 bottom
Btw, Fig. 1. shows no trackways, just a phylogenetic tree.
Peter Nyikos
pnyikos
> On 29/08/11 18:13, pnyikos wrote:
>
>
>
>
>
> > In the 7 January 2010 issue of _Nature_, there is a pair of articles
> > about what appear to be tetrapod trackways that predate such well-
> > known tranisitional fish fossils as those we have of Eusthenopteron,
> > Panderichthys, and Tiktaalik:
>
> >http://www.nature.com/nature/journal/v463/n7277/full/463040a.html
> >http://www.nature.com/nature/journal/v463/n7277/full/nature08623.html
> >http://www.nature.com/nature/journal/v463/n7277/covers/
>
> > You may need to pay for these, so here are two popularizations
> > available for free:
>
> > linked from:
> >http://dinosaurs.about.com/b/2010/01/07/the-400-million-year-old-tetr...
>
> > The favored explanation for the discrepancy, reminiscent of the
> > similarly big gap for the first birds vs Dromaesaurs, is that
> > Eusthenopteron, Panderichthys, and Tiktaalik are "relicts" from an
> > earlier era where very similar transitional forms exist.
>
> > But I can think of several others, and my interpretation of the
> > trackways is not adequate to settle the first one:
>
> > 1. These tracks represent a parallel evolution of a "failed
> > experiment" in tetrapody.
>
> What do you mean by that ?
That the trackways were made not by any descendant of the sister group
of tetrapods [not to be confused with Tetrapoda, a label whose
assignment is a subject of heated controversy], the Elpistostegalians,
but by the descendants of some more distantly related fish.
> At all times species contain many many
> individuals and many many related species coexist, only one of which can
> be the common ancestor of any future group, so it's obvious that
> tetrapody involved a whole lot of "failed experiments", i.e. some
> members of the proto-tetrapod group that remained proto-tetrapods until
> they went extinct and didn't spawn the actual tetrapods,
You are talking about cladogenesis. The relevant proto-tetrapod group
here is not a population, nor a species, but something more general.
> or spawned
> close cousins that went extinct. That's the same thing as saying that
> Tiktaalik et al are "relics" from an earlier era.
>
> If by "parallel evolution" you actually mean other groups completely
> unrelated to the group that spawned tetrapods evolving into
> tetrapod-like creatures and disappearing, well, it's possible, but
> there's no evidence for it.
Think of mudskippers, totally unrelated to the fishes we are talking
about. I have in mind something much closer to them in 1.
> More than that, given in this case we're
> hypothesising an *earlier* parallel group (in fact it's specifically to
> explain why these tracks are so early that you're suggesting a parallel
> group) I'd expect the opposite to happen. If a group starts exploiting a
> new niche and is successful at it (say, successful enough that they
> leave evidence in the form of fossil tracks)
That isn't huge success. A small asteroid could wipe them out.
> they'll tend to radiate and
> occupy the niche and make it more difficult for other groups to evolve
> the same way later.
See my reply to Harshman for my take on 2 and 3.
Peter Nyikos
John Harshman
The more detail we can see in the trackway, the less likely. Agreed? And
the fact that we know of tetrapods but don't know of any ancient
non-tetrapod walking fish is also some evidence. Would you agree?
pnyikos
> pnyikos wrote:
> > On Aug 29, 5:10 pm, John Harshman <jharsh...@pacbell.net> wrote:
> >> pnyikos wrote:
> >>> In the 7 January 2010 issue of _Nature_, there is a pair of articles
> >>> about what appear to be tetrapod trackways that predate such well-
> >>> known tranisitional fish fossils as those we have of Eusthenopteron,
> >>> Panderichthys, and Tiktaalik:
> >>>http://www.nature.com/nature/journal/v463/n7277/full/463040a.html
> >>>http://www.nature.com/nature/journal/v463/n7277/full/nature08623.html
Here is a very nice website on Tiktaalik, showing how it seems to be
an ideal transitional between Eusthenopteron and Panderichthys on the
one hand, and the tetrapods on the other.
http://chronicle.uchicago.edu/081023/tiktaalik.shtml
[...]
> >>> The favored explanation for the discrepancy, reminiscent of the
> >>> similarly big gap for the first birds vs Dromaesaurs, is that
> >>> Eusthenopteron, Panderichthys, and Tiktaalik are "relicts" from an
> >>> earlier era where very similar transitional forms exist.
> >>> But I can think of several others, and my interpretation of the
> >>> trackways is not adequate to settle the first one:
> >>> 1. These tracks represent a parallel evolution of a "failed
> >>> experiment" in tetrapody.
> >>> 2. The "tracks" are natural geological formations, like the
> >>> "footprint" of "Thinopus".
> >>> 3. The trackway has been improperly dated.
> >>> Can anyone help decide between the above four possibilities, or argue
> >>> for yet others? "possibility zero" is the favored explanation I gave
> >>> above.
> >> All are conceivable explanations, though 2 and 3 seem unlikely unless
> >> you have some argument for either of them.
>
> > And I don't. The second article does what looks like a good job of
> > taking care of 3, and its case for 2. being false looks convincing.
>
> >> 0 seems best. Do you have a
> >> preference?
>
> > Mine is for 0 also, though 1. is an intriguing possibility.
>
> The more detail we can see in the trackway, the less likely. Agreed?
Only if the details are very similar to those of prints of
*Acanthostega*, *Ichthyostega*, or other confirmed tetrapods.
By the way, it is nice to see how I am not the only one who dislikes
the idea of making Tetrapoda the designation of a comparatively small
crown group based on extant species. Ahlberg is another, and so is
Jennifer A. Clack:
The author disagrees with the move to restrict
the vernacular term ‘tetrapod’ to a crown clade
(Gauthier et al. 1989). In this page, the term
‘tetrapod’ and ‘stem-tetrapod’ refer only to
vertebrates with limbs and digits.
http://tolweb.org/Ichthyostega/15015
> And
> the fact that we know of tetrapods but don't know of any ancient
> non-tetrapod walking fish is also some evidence. Would you agree?
If the tracks are different--and it looks to me that the authors are
overstating the case for the similarity -- then we have to balance
this against the fact that our *Tiktaalik* fossils come later in time
than those of the fish that it represents the next step from on the
way to tetrapods. Why should these "relicts" show up in the order in
which they supposedly arose over ten million years earlier?
And *Tiktaalik* really looks like a fine transitional from
Eusthenopteron types to tetrapods. I refer you not only to the
University of Chicago website above but also to the two seminal
articles on this theme:
(6 April 2006):
http://www.nature.com/nature/journal/v440/n7085/pdf/nature04639.pdf
(16 October 2008):
http://www.nature.com/nature/journal/v455/n7215/full/nature07189.html
The authors of the main article don't do a very good job of meeting
that objection:
...why do the elpistostegids appear before
tetrapods in the body fossil record in a manner
that neatly simulates a stratophylogenetic fit (Fig. 5)?
...
If their first appearance as body fossils reflects
the time when they first colonized environments
with preservation potential, as seems likely, the
elpistostegids evidently arrived in advance of the
tetrapods. The reason was presumably ecological
but cannot be determined at present.
http://www.nature.com/nature/journal/v463/n7277/full/nature08623.html
Peter Nyikos
Arkalen
Looks like we're thinking of the same thing. So, again: no evidence for it.
>
>> More than that, given in this case we're
>> hypothesising an *earlier* parallel group (in fact it's specifically to
>> explain why these tracks are so early that you're suggesting a parallel
>> group) I'd expect the opposite to happen. If a group starts exploiting a
>> new niche and is successful at it (say, successful enough that they
>> leave evidence in the form of fossil tracks)
>
> That isn't huge success. A small asteroid could wipe them out.
Right, that's one thing I thought of afterwards but neglected to put in:
if said first successful group (and given the tiny odds of any
individual leaving a fossil which we happen to have found, I'd say any
group that left such fossils was successful enough for our purposes)
suffers an extinction event before the later group gets into the same
niche. For this case I think climate change is a good candidate. But
such extinction events leave traces; are there any here ?
Arkalen
It makes sense to me; think of it a bit like the tide rising. The waves
always have a low point, and the low point is always lower than the high
point, but as the tide rises both the high and low points go up.
Not a great metaphor because the processes are different of course. I
assume that one reason the proto-tetrapods went extinct is because they
were outcompeted by their more-tetrapod-like descendents. It makes sense
to me: a fish that's a teeny bit adapted to land is outcompeted in the
water by fish that are absolutely adapted to the water, but it can
flourish by exploiting the unoccupied niche "stay a teeny bit on land".
Once it has to *also* compete with its teeny bit better land-adapted
descendents however it's outcompeted on both sides and goes extinct. Of
course there are always creatures that exploit transitional lifestyles,
like the lungfish, but we're talking about a group of closely-related
animals living in the same environment. They'd all be similar and
competition would be fierce between each variant.
If that's how it works, it also makes sense that the "transitional
forms" would go extinct in succession as the better-adapted forms
appeared, until the outer bound of "land-adapted" was reached and all
the transitional niches were occupied by creatures who were extremely
specialised for them - and that wouldn't necessarily be the ancestral
forms who evolved at a time when the niche wasn't transitional but the
outer bound.
tl;dr : if Ichtyostega and Tiktaalik went extinct because they were
outcompeted by other fish that were better adapted to land, it makes
perfect sense that they'd go extinct AFTER said better-adapted fish had
appeared, so Tiktaalik would go extinct before Ichtyostega did.
John Harshman
Yes.
> By the way, it is nice to see how I am not the only one who dislikes
> the idea of making Tetrapoda the designation of a comparatively small
> crown group based on extant species. Ahlberg is another, and so is
> Jennifer A. Clack:
> The author disagrees with the move to restrict
> the vernacular term ‘tetrapod’ to a crown clade
> (Gauthier et al. 1989). In this page, the term
> ‘tetrapod’ and ‘stem-tetrapod’ refer only to
> vertebrates with limbs and digits.
> http://tolweb.org/Ichthyostega/15015
Don't confuse "Tetrapoda" with "tetrapod". Clack is talking about the
latter.
>> And
>> the fact that we know of tetrapods but don't know of any ancient
>> non-tetrapod walking fish is also some evidence. Would you agree?
>
> If the tracks are different--and it looks to me that the authors are
> overstating the case for the similarity -- then we have to balance
> this against the fact that our *Tiktaalik* fossils come later in time
> than those of the fish that it represents the next step from on the
> way to tetrapods. Why should these "relicts" show up in the order in
> which they supposedly arose over ten million years earlier?
Better question: why shouldn't they? We're talking about a handful of
fossils, for which any order would be likely enough even if it were random.
> And *Tiktaalik* really looks like a fine transitional from
> Eusthenopteron types to tetrapods. I refer you not only to the
> University of Chicago website above but also to the two seminal
> articles on this theme:
> (6 April 2006):
> http://www.nature.com/nature/journal/v440/n7085/pdf/nature04639.pdf
> (16 October 2008):
> http://www.nature.com/nature/journal/v455/n7215/full/nature07189.html
Yes, and dromaeosaurs are fine transitionals too despite being mostly
much later than Archaeopteryx. So?
pnyikos
> On 30/08/11 11:45, pnyikos wrote:
>
>
>
> > On Aug 29, 7:45 pm, John Harshman <jharsh...@pacbell.net> wrote:
> >> pnyikos wrote:
> >>> On Aug 29, 5:10 pm, John Harshman <jharsh...@pacbell.net> wrote:
> >>>> pnyikos wrote:
> >>>>> In the 7 January 2010 issue of _Nature_, there is a pair of articles
> >>>>> about what appear to be tetrapod trackways that predate such well-
> >>>>> known tranisitional fish fossils as those we have of Eusthenopteron,
> >>>>> Panderichthys, and Tiktaalik:
> >>>>>http://www.nature.com/nature/journal/v463/n7277/full/463040a.html
> >>>>>http://www.nature.com/nature/journal/v463/n7277/full/nature08623.html
>
> > Here is a very nice website on Tiktaalik, showing how it seems to be
> > an ideal transitional between Eusthenopteron and Panderichthys on the
> > one hand, and the tetrapods on the other.
> >http://chronicle.uchicago.edu/081023/tiktaalik.shtml
> > [...]
> >>>>> The favored explanation for the discrepancy, reminiscent of the
> >>>>> similarly big gap for the first birds vs Dromaesaurs, is that
> >>>>> Eusthenopteron, Panderichthys, and Tiktaalik are "relicts" from an
> >>>>> earlier era where very similar transitional forms exist.
This is called "alternative 0" below.
> >>>>> But I can think of several others, and my interpretation of the
> >>>>> trackways is not adequate to settle the first one:
> >>>>> 1. These tracks represent a parallel evolution of a "failed
> >>>>> experiment" in tetrapody.
I deleted the remaining alternatives, since none of them is being
taken seriously by anyone. But here is a major variation on 1: it is
the fishes whose fossils we have, and which come later in time, that
are the "failed experiment."
And then, one of two things is likely:
a. *Ichthyostega* and *Acanthostega*, generally considered to be
tetrapods (but not members of *Tetrapoda*) are very similar to the
critters that made the trackways, and are direct descendants of
tetrapods of that early era ca. 395mya when the footprints were made
b. these two amphibious vertebrates were themselves part of the failed
experiment that began with the likes of *Eusthenopteron*,
*Panderichthys*, and *Tiktaalik*; and the tetrapods of 395mya that
gave rise to the tetrapods of the Carboniferous era. *Pederpes* and
*Whatcheeria* are two of the earliest known, fitting right in the
middle of "Romer's gap":
http://news.nationalgeographic.com/news/2002/07/0703_020703_TVtetrapod.html
http://palaeontology.palass-pubs.org/pdf/Vol%2038/Pages%20471-494.pdf
The latter website depicts *Whatcheeria* as being on the way to
amniotes, in a clade that excludes most of the amphibians of the
Carboniferous. But I've seen another website which claims
*Whatcheeria* is very similar to *Pederpes*.
> >>> Mine is for 0 also, though 1. is an intriguing possibility.
>
> >> The more detail we can see in the trackway, the less likely. Agreed?
>
> > Only if the details are very similar to those of prints of
> > *Acanthostega*, *Ichthyostega*, or other confirmed tetrapods.
[...]
> >> And
> >> the fact that we know of tetrapods but don't know of any ancient
> >> non-tetrapod walking fish is also some evidence. Would you agree?
>
> > If the tracks are different--and it looks to me that the authors are
> > overstating the case for the similarity -- then we have to balance
> > this against the fact that our *Tiktaalik* fossils come later in time
> > than those of the fish that it represents the next step from on the
> > way to tetrapods. Why should these "relicts" show up in the order in
> > which they supposedly arose over ten million years earlier?
> It makes sense to me; think of it a bit like the tide rising. The waves
> always have a low point, and the low point is always lower than the high
> point, but as the tide rises both the high and low points go up.
>
> Not a great metaphor because the processes are different of course. I
> assume that one reason the proto-tetrapods went extinct is because they
> were outcompeted by their more-tetrapod-like descendents.
The proto-tetrapods that made those tracks would have been at about
the same grade as *Ichthyostega* and *Acanthostega*. AFAIK, the
first fossils we have of more-tetrapod-like descendants are those of
*Pederpes* and *Whatcheeria*.
So your statements above seem to be beside the point of how we resolve
the status of *Tiktaalik* and its precursors. But the ones you made
below [deleted] are more relevant to that point.
I'll address those in my next reply.
Peter Nyikos
pnyikos
I am repeating a bit from my previous reply.
> > Why should these "relicts" show up in the order in
> > which they supposedly arose over ten million years earlier?
Those "relicts" include *Eusthenopteron*, *Panderichthys*, and
*Tiktaalik*, in that order. Even the last is not a tetrapod, though
it is closer to tetrapody than the first two.
> It makes sense to me; think of it a bit like the tide rising. The waves
> always have a low point, and the low point is always lower than the high
> point, but as the tide rises both the high and low points go up.
>
> Not a great metaphor because the processes are different of course. I
> assume that one reason the proto-tetrapods went extinct is because they
> were outcompeted by their more-tetrapod-like descendents.
I now realize that I probably misread what you wrote above when I
replied:
"The proto-tetrapods that made those tracks would have been at about
the same grade as *Ichthyostega* and *Acanthostega*. AFAIK, the
first fossils we have of more-tetrapod-like descendants are those of
*Pederpes* and *Whatcheeria*."
Actually, the latter two are undeniably tetrapods, and the former two
are often thought of as tetrapods, and so perhaps you meant the genera
listed below all along.
> It makes sense
> to me: a fish that's a teeny bit adapted to land
like *Tiktaalik*
> is outcompeted in the
> water by fish that are absolutely adapted to the water,
like *Eusthenopteron*
I chose these two because they receive star billing in the University
of Chicago website along with *Acanthostega*:
http://chronicle.uchicago.edu/081023/tiktaalik.shtml
> but it can
> flourish by exploiting the unoccupied niche "stay a teeny bit on land".
But if the creatures that made those trackways were NOT a "failed
experiment" in tetrapody, then the niche would NOT be unoccupied--it
would have been exploited for 20 million years at least--plenty of
time for the tetrapods of ca. 395mya to spread out over whatever
continents they arose in or near.
> Once it has to *also* compete with its teeny bit better land-adapted
> descendents however it's outcompeted on both sides and goes extinct. Of
> course there are always creatures that exploit transitional lifestyles,
> like the lungfish, but we're talking about a group of closely-related
> animals living in the same environment. They'd all be similar and
> competition would be fierce between each variant.
This is all fine and dandy, but how do you relate it to the actual
species of which we are talking? you seem to have left the creatures
that made those tracks ca. 395 mya out in the cold.
> If that's how it works, it also makes sense that the "transitional
> forms" would go extinct in succession as the better-adapted forms
> appeared, until the outer bound of "land-adapted" was reached and all
> the transitional niches were occupied by creatures who were extremely
> specialised for them - and that wouldn't necessarily be the ancestral
> forms who evolved at a time when the niche wasn't transitional but the
> outer bound.
More of the same.
> tl;dr : if Ichtyostega and Tiktaalik went extinct because they were
> outcompeted by other fish
I don't think any paleontologist thinks of *Ichthyostega* as a fish.
OTOH *Eusthenopteron*, *Panderichthys*, and *Tiktaalik* are generally
referred to as fishes.
> that were better adapted to land, it makes
> perfect sense that they'd go extinct AFTER said better-adapted fish had
> appeared, so Tiktaalik would go extinct before Ichtyostega did.
We aren't so concerned about the *last* appearance of these critters
as we are of the *first*. All the genera mentioned above *appeared*
well after those trackways were made, unless they were essentially
"living fossils" of the time.
The seminal _Nature_ article on the pathways tries to make a case for
the critters who made the tracks being very similar to
*Ichthyostega*. But we have nothing to hint of anything like *any* of
the genera I mentioned before this time.
Why, those pathways even predate *Osteolepis*, a lobefin fish widely
cited as being less tetrapod-like even than *Eusthenopteron*, and
generally believed to be very much like an ancestor of the latter.
Peter Nyikos
pnyikos
> pnyikos wrote:
> > On Aug 29, 7:45 pm, John Harshman <jharsh...@pacbell.net> wrote:
> >> pnyikos wrote:
> >>> On Aug 29, 5:10 pm, John Harshman <jharsh...@pacbell.net> wrote:
> >>>> pnyikos wrote:
> >>>>> In the 7 January 2010 issue of _Nature_, there is a pair of articles
> >>>>> about what appear to be tetrapod trackways that predate such well-
> >>>>> known tranisitional fish fossils as those we have of Eusthenopteron,
> >>>>> Panderichthys, and Tiktaalik:
> >>>>>http://www.nature.com/nature/journal/v463/n7277/full/463040a.html
> >>>>>http://www.nature.com/nature/journal/v463/n7277/full/nature08623.html
The latter is the seminal article; the former is a commentary on it,
menitioning other articles in passing.
> >>>>> The favored explanation for the discrepancy, reminiscent of the
> >>>>> similarly big gap for the first birds vs Dromaesaurs, is that
> >>>>> Eusthenopteron, Panderichthys, and Tiktaalik are "relicts" from an
> >>>>> earlier era where very similar transitional forms exist.
This was referred to as "alternative 0" below.
> >>>>> But I can think of several others, and my interpretation of the
> >>>>> trackways is not adequate to settle the first one:
> >>>>> 1. These tracks represent a parallel evolution of a "failed
> >>>>> experiment" in tetrapody.
[...]
> >>>> 0 seems best. Do you have a
> >>>> preference?
> >>> Mine is for 0 also, though 1. is an intriguing possibility.
> >> The more detail we can see in the trackway, the less likely. Agreed?
>
> > Only if the details are very similar to those of prints of
> > *Acanthostega*, *Ichthyostega*, or other confirmed tetrapods.
>
> Yes.
I'm glad we agree on this much. It looks to me like the authors of
the seminal _Nature_ article on the trackways were taking considerable
liberties when reconstructing how the soft parts of the pes of
*Ichthyostega* looked; they were obviously trying to make a case for
the tetrapods that made the tracks being very much like
*Ichthyostega*.
> > By the way, it is nice to see how I am not the only one who dislikes
> > the idea of making Tetrapoda the designation of a comparatively small
> > crown group based on extant species. Ahlberg is another, and so is
> > Jennifer A. Clack:
> > The author disagrees with the move to restrict
> > the vernacular term ‘tetrapod’ to a crown clade
> > (Gauthier et al. 1989). In this page, the term
> > ‘tetrapod’ and ‘stem-tetrapod’ refer only to
> > vertebrates with limbs and digits.
> >http://tolweb.org/Ichthyostega/15015
>
> Don't confuse "Tetrapoda" with "tetrapod". Clack is talking about the
> latter.
You are obviously addressing the general readership; you can see I
need no such reminder.
> >> And
> >> the fact that we know of tetrapods but don't know of any ancient
> >> non-tetrapod walking fish is also some evidence. Would you agree?
>
> > If the tracks are different--and it looks to me that the authors are
> > overstating the case for the similarity -- then we have to balance
> > this against the fact that our *Tiktaalik* fossils come later in time
> > than those of the fish that it represents the next step from on the
> > way to tetrapods. Why should these "relicts" show up in the order in
> > which they supposedly arose over ten million years earlier?
>
> Better question: why shouldn't they? We're talking about a handful of
> fossils, for which any order would be likely enough even if it were random.
This "handful" includes *Osteolepis*, *Eusthenopteron,*
*Panderichthys* and *Tiktaalik* in that order. Already odds of 15 to
1 against their fossils having come down to us in the same order in
which they first appeared. Add to that all the other crossopterygians
that seem to belong to this general progression, all postdating those
tracks, and you can see why I think alternative 1. is a very strong
possibility.
By the way, what do you think of alternatives a. and b. that I
mentioned in my first reply to Arkalen today? They are variations on
an alternative way of explaining the progression we see in the
"handful".
Peter Nyikos
John Harshman
Actually, I can't see that, since you use a statement about "tetrapods"
to support a claim about "Tetrapoda".
>>>> And
>>>> the fact that we know of tetrapods but don't know of any ancient
>>>> non-tetrapod walking fish is also some evidence. Would you agree?
>>> If the tracks are different--and it looks to me that the authors are
>>> overstating the case for the similarity -- then we have to balance
>>> this against the fact that our *Tiktaalik* fossils come later in time
>>> than those of the fish that it represents the next step from on the
>>> way to tetrapods. Why should these "relicts" show up in the order in
>>> which they supposedly arose over ten million years earlier?
>> Better question: why shouldn't they? We're talking about a handful of
>> fossils, for which any order would be likely enough even if it were random.
>
> This "handful" includes *Osteolepis*, *Eusthenopteron,*
> *Panderichthys* and *Tiktaalik* in that order.
Really? I was unaware that the order was that good. Can you give me a
reference?
> Already odds of 15 to
> 1 against their fossils having come down to us in the same order in
> which they first appeared. Add to that all the other crossopterygians
> that seem to belong to this general progression, all postdating those
> tracks, and you can see why I think alternative 1. is a very strong
> possibility.
No, still can't. In order to make the claim you have to suppose that the
fossil record is very good throughout the relevant period. Do you think
it is?
> By the way, what do you think of alternatives a. and b. that I
> mentioned in my first reply to Arkalen today? They are variations on
> an alternative way of explaining the progression we see in the
> "handful".
Dunno. Haven't looked. I don't read everything.
Arkalen
I thought of that variant but it's even less likely than the first.
IANAP but when palaeontologists look at ancient fish skeletons they
don't just go "hey those four fins look kind of like four legs,
proto-tetrapod score !". They look at the whole skeleton and find
similarities in the skull, fin structure, all over the place between
that specimen, tetrapods in general and other similar fossils.
So when people say that Tiktaalik is a proto-tetrapod (relic that it may
be) I'm fairly certain they're not saying "we've got four legs,
Tiktaalik has almost four legs, we must be related !", they're saying
"this fish has a suite of characters that make it look related to
tetrapods. As a bonus, it almost has four legs !"
You yourself specified that by "parallel branch" you meant a totally
different group of fish, like mudskippers. Mudskippers don't look like
descendents of Tiktaalik, and it's not just because they have two "legs"
instead of four. If Tiktaalik belonged to such a parallel line it would
be quite different from tetrapods in basic ways.
>
> And then, one of two things is likely:
>
> a. *Ichthyostega* and *Acanthostega*, generally considered to be
> tetrapods (but not members of *Tetrapoda*) are very similar to the
> critters that made the trackways, and are direct descendants of
> tetrapods of that early era ca. 395mya when the footprints were made
>
> b. these two amphibious vertebrates were themselves part of the failed
> experiment that began with the likes of *Eusthenopteron*,
> *Panderichthys*, and *Tiktaalik*; and the tetrapods of 395mya that
> gave rise to the tetrapods of the Carboniferous era. *Pederpes* and
> *Whatcheeria* are two of the earliest known, fitting right in the
> middle of "Romer's gap":
>
> http://news.nationalgeographic.com/news/2002/07/0703_020703_TVtetrapod.html
>
> http://palaeontology.palass-pubs.org/pdf/Vol%2038/Pages%20471-494.pdf
>
> The latter website depicts *Whatcheeria* as being on the way to
> amniotes, in a clade that excludes most of the amphibians of the
> Carboniferous. But I've seen another website which claims
> *Whatcheeria* is very similar to *Pederpes*.
So ? They're still both considered Tetrapoda. Is there any evidence that
they (or another of the specimens you mention) belong to some parallel,
unrelated line ? By "unrelated" here of course I mean "whose common
ancestor with Tetrapoda goes back long before the first vertebrate set
fin on land", such as is the case with mudskippers.
I'm afraid I don't see what that has to do with what I was saying, but
see you next post then.
Arkalen
I don't think you understand what I'm saying at all, or more likely I
misunderstood your original question. You asked why organisms like
Ichtyostega and Tiktaalik appeared long after the tracks but *in the
order we'd expect them to appear in if they'd been our direct
ancestors*. It's the second point I was addressing, not the first. For
the first, well, what are the odds that the first transitional fossils
we found happened to be the first that had appeared ? Of course some
fossils we discover will appear to be in the wrong order.
The two points look contradictory but they aren't really; I see it as a
question of probabilities. As John pointed out species don't go extinct
instantly in an orderly fashion so it's normal we'd find some "more
advanced" species occurring before some "less advanced" specimens we'd
expect to be the former's ancestors (and might be, they just hung around
a long time). All my tangent about rising tides was meant to explain is
why, despite that fact, we might have higher odds of finding "more
advanced" species after the "less advanced" ones, so seeing it occur
isn't that surprising either.
>
>> If that's how it works, it also makes sense that the "transitional
>> forms" would go extinct in succession as the better-adapted forms
>> appeared, until the outer bound of "land-adapted" was reached and all
>> the transitional niches were occupied by creatures who were extremely
>> specialised for them - and that wouldn't necessarily be the ancestral
>> forms who evolved at a time when the niche wasn't transitional but the
>> outer bound.
>
> More of the same.
>
>> tl;dr : if Ichtyostega and Tiktaalik went extinct because they were
>> outcompeted by other fish
>
> I don't think any paleontologist thinks of *Ichthyostega* as a fish.
> OTOH *Eusthenopteron*, *Panderichthys*, and *Tiktaalik* are generally
> referred to as fishes.
>
>> that were better adapted to land, it makes
>> perfect sense that they'd go extinct AFTER said better-adapted fish had
>> appeared, so Tiktaalik would go extinct before Ichtyostega did.
>
> We aren't so concerned about the *last* appearance of these critters
> as we are of the *first*.
I don't see how. You seem to wonder why we'd find tetrapod tracks, and
then much later we'd find a few specimens of proto-tetrapods that are
more primitive than those that left the tracks, but other than that
appear in the expected order of primitiveness.
Well, the answer to that doesn't depend on when any of those specimens
*first* appeared, it depends on their *range* : for how long did they
exist ? So their last appearance is just as important as their first
appearance if we're surprised at finding their fossils where we did find
them.
pnyikos
I see the role of the word "designation" escaped your attention.
Apparently I should have put "Tetrapoda" into scare quotes. [Thanks
for teaching me the meaning of the term "scare quotes", btw.]
> >>>> And
> >>>> the fact that we know of tetrapods but don't know of any ancient
> >>>> non-tetrapod walking fish is also some evidence. Would you agree?
> >>> If the tracks are different--and it looks to me that the authors are
> >>> overstating the case for the similarity -- then we have to balance
> >>> this against the fact that our *Tiktaalik* fossils come later in time
> >>> than those of the fish that it represents the next step from on the
> >>> way to tetrapods. Why should these "relicts" show up in the order in
> >>> which they supposedly arose over ten million years earlier?
> >> Better question: why shouldn't they? We're talking about a handful of
> >> fossils, for which any order would be likely enough even if it were random.
>
> > This "handful" includes *Osteolepis*, *Eusthenopteron,*
> > *Panderichthys* and *Tiktaalik* in that order.
>
> Really? I was unaware that the order was that good. Can you give me a
> reference?
For the last two, the seminal trackway article itself is a good one,
and here is an url for the relevant illustration:
http://www.nature.com/nature/journal/v463/n7277/fig_tab/nature08623_F5.html
The fact that *Osteolepis* came before *Eusthenopteron* is cited in
Romer's old _Vertebrate Paleontology_ and is also confirmed by a
similar illustration in the companion article,
http://www.nature.com/nature/journal/v463/n7277/full/463040a.html
As for *E* and *P* the following put them at 385 and 380 mya
respectively:
http://dinosaurs.about.com/od/tetrapodsandamphibians/p/eusthenopteron.htm
http://dinosaurs.about.com/od/tetrapodsandamphibians/p/panderichthys.htm
The whole sequence, minus dates, can be found as part of a much more
detailed sequence in:
http://www.biology.ualberta.ca/courses.hp/biol606/papers/Ahlberg+1998.pdf
> > Already odds of 15 to
> > 1 against their fossils having come down to us in the same order in
> > which they first appeared. Add to that all the other crossopterygians
> > that seem to belong to this general progression, all postdating those
> > tracks, and you can see why I think alternative 1. is a very strong
> > possibility.
>
> No, still can't. In order to make the claim you have to suppose that the
> fossil record is very good throughout the relevant period.
Wrong. I was thinking pragmatically, based on the available
evidence. Just like you do with the term "sister group".
The seminal article makes it clear that the fossil record is scanty
but it also makes it clear that this does not resolve the problem of
stratophylogenetic fit:
"The absence of tetrapods in these deposits may simply be a matter of
environmental preference. The false stratophylogenetic succession from
elpistostegids to tetrapods is more of a puzzle. If their first
appearance as body fossils reflects the time when they first colonized
environments with preservation potential, as seems likely, the
elpistostegids evidently arrived in advance of the tetrapods. The
reason was presumably ecological but cannot be determined at present."
At that, they understate the puzzle, since they mention neither
Osteolepis nor Eusthenopteron (nor, more precisely, the groups to
which these belong).
Peter Nyikos
Rolf
The coelecanth went extinct 65 million years ago, except it didn't. I still
remember reading about it in 1938 although I didn't understand it.
Rolf
pnyikos
Wow, you are a real old-timer! I wasn't even born until eight years
later.
I did read about the second coelacanth three years after it was
caught. One of my prized possessions is a book given to me on my 12th
birthday by my late father, written by the discoverer, J.L.B. Smith,
_The Search Beneath the Sea_ , about his 14-year long hunt for a good
specimen. The first one was just skin and skull by the time he got to
it.
Anyway, since the coelacanth is not assumed to be close to the
ancestry of any tetrapods, it's not the best analogy to the puzzle
facing the track-discoverers.
Peter Nyikos
Rolf
Right, I just find it interesting as an apropos to the incompleteness of the
fossil record.
> Peter Nyikos
John Harshman
I don't understand what you were attempting to convey by "designation".
I don't, apparently, understand your point at all here.
>>>>>> And
>>>>>> the fact that we know of tetrapods but don't know of any ancient
>>>>>> non-tetrapod walking fish is also some evidence. Would you agree?
>>>>> If the tracks are different--and it looks to me that the authors are
>>>>> overstating the case for the similarity -- then we have to balance
>>>>> this against the fact that our *Tiktaalik* fossils come later in time
>>>>> than those of the fish that it represents the next step from on the
>>>>> way to tetrapods. Why should these "relicts" show up in the order in
>>>>> which they supposedly arose over ten million years earlier?
>>>> Better question: why shouldn't they? We're talking about a handful of
>>>> fossils, for which any order would be likely enough even if it were random.
>>> This "handful" includes *Osteolepis*, *Eusthenopteron,*
>>> *Panderichthys* and *Tiktaalik* in that order.
>> Really? I was unaware that the order was that good. Can you give me a
>> reference?
>
> For the last two, the seminal trackway article itself is a good one,
> and here is an url for the relevant illustration:
>
> http://www.nature.com/nature/journal/v463/n7277/fig_tab/nature08623_F5.html
Not bad, though hardly perfect. Livoniana, at least, is out of order.
> The fact that *Osteolepis* came before *Eusthenopteron* is cited in
> Romer's old _Vertebrate Paleontology_ and is also confirmed by a
> similar illustration in the companion article,
True. But you fail to note that Eusthenopteron is at best contemporary
with Panderichthys and may in fact slightly postdate it.
> http://www.nature.com/nature/journal/v463/n7277/full/463040a.html
Can't see that one. Paywall.
> As for *E* and *P* the following put them at 385 and 380 mya
> respectively:
>
> http://dinosaurs.about.com/od/tetrapodsandamphibians/p/eusthenopteron.htm
>
> http://dinosaurs.about.com/od/tetrapodsandamphibians/p/panderichthys.htm
>
> The whole sequence, minus dates, can be found as part of a much more
> detailed sequence in:
>
> http://www.biology.ualberta.ca/courses.hp/biol606/papers/Ahlberg+1998.pdf
Not a sequence, but a branching tree. You can only turn it into a
sequence by supposing there's a "main line" and "side branches". And
without dates, there's no relevance here.
>>> Already odds of 15 to
>>> 1 against their fossils having come down to us in the same order in
>>> which they first appeared. Add to that all the other crossopterygians
>>> that seem to belong to this general progression, all postdating those
>>> tracks, and you can see why I think alternative 1. is a very strong
>>> possibility.
>> No, still can't. In order to make the claim you have to suppose that the
>> fossil record is very good throughout the relevant period.
>
> Wrong. I was thinking pragmatically, based on the available
> evidence. Just like you do with the term "sister group".
Please don't try to equate this. And in fact you are picking and
choosing. You have taken a few fossils from a complex tree to represent
some kind of "main line", and you have picked ones that also (mostly)
fit your timeline. You could have picked others that don't fit. I can't
say your inference is entirely invalid, but there are clear problems
with it.
> The seminal article makes it clear that the fossil record is scanty
> but it also makes it clear that this does not resolve the problem of
> stratophylogenetic fit:
>
> "The absence of tetrapods in these deposits may simply be a matter of
> environmental preference. The false stratophylogenetic succession from
> elpistostegids to tetrapods is more of a puzzle. If their first
> appearance as body fossils reflects the time when they first colonized
> environments with preservation potential, as seems likely, the
> elpistostegids evidently arrived in advance of the tetrapods. The
> reason was presumably ecological but cannot be determined at present."
>
> At that, they understate the puzzle, since they mention neither
> Osteolepis nor Eusthenopteron (nor, more precisely, the groups to
> which these belong).
It would be better to concentrate on characters. The earliest
representation of a character is more likely to represent an
evolutionary sequence than any particular set of taxa, just because
there is better sampling for the character than for any particular taxon.
pnyikos
"Tetrapoda" was stuck onto a crown group that leaves out a hell of a
lot of tetrapods, see? Clack doesn't like slapping that label on such
a restricted set of tetrapods. Capice?
And months ago, I was already complaining to you about the same
identical slapping-on, remember?
>
> >>>>>> And
> >>>>>> the fact that we know of tetrapods but don't know of any ancient
> >>>>>> non-tetrapod walking fish is also some evidence. Would you agree?
> >>>>> If the tracks are different--and it looks to me that the authors are
> >>>>> overstating the case for the similarity -- then we have to balance
> >>>>> this against the fact that our *Tiktaalik* fossils come later in time
> >>>>> than those of the fish that it represents the next step from on the
> >>>>> way to tetrapods. Why should these "relicts" show up in the order in
> >>>>> which they supposedly arose over ten million years earlier?
> >>>> Better question: why shouldn't they? We're talking about a handful of
> >>>> fossils, for which any order would be likely enough even if it were random.
> >>> This "handful" includes *Osteolepis*, *Eusthenopteron,*
> >>> *Panderichthys* and *Tiktaalik* in that order.
> >> Really? I was unaware that the order was that good. Can you give me a
> >> reference?
>
> > For the last two, the seminal trackway article itself is a good one,
> > and here is an url for the relevant illustration:
>
> Not bad, though hardly perfect. Livoniana, at least, is out of order.
> > The fact that *Osteolepis* came before *Eusthenopteron* is cited in
> > Romer's old _Vertebrate Paleontology_ and is also confirmed by a
> > similar illustration in the companion article,
>
> True. But you fail to note that Eusthenopteron is at best contemporary
> with Panderichthys and may in fact slightly postdate it.
> > As for *E* and *P* the following put them at 385 and 380 mya
> > respectively:
>
>
> > http://dinosaurs.about.com/od/tetrapodsandamphibians/p/panderichthys.htm
Do you have a reference that reverses them?
> > The whole sequence, minus dates, can be found as part of a much more
> > detailed sequence in:
>
> Not a sequence, but a branching tree. You can only turn it into a
> sequence by supposing there's a "main line" and "side branches".
sequence" from *Hyracotherium* to *Equus* while ignorig the "side
branches," even though a case could be made for the "main line" ending
in *Hypohippus*?
Remainder deleted, to be repied to later.
Peter Nyikos
John Harshman
>>>>>>> (Gauthier et al. 1989). In this page, the term
>>>>>>> vertebrates with limbs and digits.
>>>>>>> http://tolweb.org/Ichthyostega/15015
>>>>>> Don't confuse "Tetrapoda" with "tetrapod". Clack is talking about the
>>>>>> latter.
>>>>> You are obviously addressing the general readership; you can see I
>>>>> need no such reminder.
>>>> Actually, I can't see that, since you use a statement about "tetrapods"
>>>> to support a claim about "Tetrapoda".
>>> I see the role of the word "designation" escaped your attention.
>>> Apparently I should have put "Tetrapoda" into scare quotes. [Thanks
>>> for teaching me the meaning of the term "scare quotes", btw.]
>> I don't understand what you were attempting to convey by "designation".
>> I don't, apparently, understand your point at all here.
>
> Y'see, it's dis way. A designation is like a label, see? The label
> "Tetrapoda" was stuck onto a crown group that leaves out a hell of a
> lot of tetrapods, see? Clack doesn't like slapping that label on such
> a restricted set of tetrapods. Capice?
I do. You have confused the two words, Tetrapoda and tetrapod. Clack is
objecting to restricting the latter, not the former. It's possible she
doesn't like the former either, but you haven't presented any quote that
says that.
> And months ago, I was already complaining to you about the same
> identical slapping-on, remember?
Who knows, since what you actually mean to say here is ambiguous. Which
is it, Tetrapoda or tetrapod, that you're objecting to?
More or less. It's a figure in Palaeobiology II, edited by Briggs &
Crowther, page 76, which is stated as being adapted from Clack 1997.
Both taxa have ranges, and Panderichthys is shown as having its range
beginning just slightly earlier. That reference is Devonian tetrapod
trackways and trackmakers: A review of the fossils and footprints.
Palaeogeography, Palaeoclimatology, Palaeoecology 130:227-250. Which I
don't have.
Your reference unfortunately doesn't give a source in the primary
literature.
>>> The whole sequence, minus dates, can be found as part of a much more
>>> detailed sequence in:
>>> http://www.biology.ualberta.ca/courses.hp/biol606/papers/Ahlberg+1998...
>> Not a sequence, but a branching tree. You can only turn it into a
>> sequence by supposing there's a "main line" and "side branches".
>
> Now it's my turn to be puzzled: don't they talk about the "horse
> sequence" from *Hyracotherium* to *Equus* while ignorig the "side
> branches," even though a case could be made for the "main line" ending
> in *Hypohippus*?
Sometimes people do. I should hope that professional paleontologists
don't do it these days, unless they're talking down to the public (and I
don't like the idea of talking down either). But no case can be made for
anything being the "main line", since there is no such thing as a main line.
Stanley Friesen
>On Sep 1, 11:40 am, John Harshman <jharsh...@pacbell.net> wrote:
>> sequence by supposing there's a "main line" and "side branches".
>
>Now it's my turn to be puzzled: don't they talk about the "horse
>sequence" from *Hyracotherium* to *Equus* while ignorig the "side
>branches," even though a case could be made for the "main line" ending
>in *Hypohippus*?
>
actual evolution of the equine clade is very, very bushy. It is just
that only one small remnant - the genus Equus - survives, so
popularizers can make a good show of imagining that the modern horse was
the "main line".
--
The peace of God be with you.
Stanley Friesen
pnyikos
> >On Sep 1, 11:40 am, John Harshman <jharsh...@pacbell.net> wrote:
> >> [snip snip]
> >> Not a sequence, but a branching tree. You can only turn it into a
> >> sequence by supposing there's a "main line" and "side branches".
>
> >Now it's my turn to be puzzled: don't they talk about the "horse
> >sequence" from *Hyracotherium* to *Equus* while ignorig the "side
> >branches," even though a case could be made for the "main line" ending
> >in *Hypohippus*?
>
> This is said by some, mostly in popular works, but it is incorrect. The
> actual evolution of the equine clade is very, very bushy.
chain of animals that threads its way through the bush, just like a
tree climber climbing out onto a limb and then a thick branch without
going any further up the trunk nor the main part of the limb.
In fact, this chain even threads its way up to the species that we
call "horse" as opposed to "donkey, ..." in the popular accounts, but
they almost never mention the species name.
> It is just
> that only one small remnant - the genus Equus - survives, so
> popularizers can make a good show of imagining that the modern horse was
> the "main line".
and zebras out in the cold.
> The peace of God be with you.
>
> Stanley Friesen
Peter Nyikos
Stanley Friesen
Actually, I was using "horse" in a generic sense, to refer to all extant
equines. Still, I admit that could easily be missed, since the word is
ambiguous - genus _Equus_ or species _Equus caballus_.
--
John Harshman
> On Sep 12, 8:02 pm, Stanley Friesen <sar...@friesen.net> wrote:
>> pnyikos <nyik...@bellsouth.net> wrote:
>>> On Sep 1, 11:40 am, John Harshman <jharsh...@pacbell.net> wrote:
>>>> [snip snip]
>>>> Not a sequence, but a branching tree. You can only turn it into a
>>>> sequence by supposing there's a "main line" and "side branches".
>>> Now it's my turn to be puzzled: don't they talk about the "horse
>>> sequence" from *Hyracotherium* to *Equus* while ignorig the "side
>>> branches," even though a case could be made for the "main line" ending
>>> in *Hypohippus*?
>> This is said by some, mostly in popular works, but it is incorrect. The
>> actual evolution of the equine clade is very, very bushy.
>
> Yes, I know. But I think "the horse sequence" ought to refer to a
> chain of animals that threads its way through the bush, just like a
> tree climber climbing out onto a limb and then a thick branch without
> going any further up the trunk nor the main part of the limb.
Please define "main part of the limb" and "trunk" in the current context.
> In fact, this chain even threads its way up to the species that we
> call "horse" as opposed to "donkey, ..." in the popular accounts, but
> they almost never mention the species name.
Because they're all Equus and not all that different from each other as
horses go. Of course we have no such chain unless you can assign actual
ancestry.
>> It is just
>> that only one small remnant - the genus Equus - survives, so
>> popularizers can make a good show of imagining that the modern horse was
>> the "main line".
>
> That's a purely subjective use of "main line". It even leaves asses
> and zebras out in the cold.
What genus do you think asses and zebras belong to, just out of curiosity?
ark...@inbox.com
learning about the linear horse evolution, and then learning that
athough it was always portrayed as a line it was actually more like a
bush. And I went to a natural history museum in London recently where
they had an exhibit on horse evolution, and it was all about showing
the side-branches and illustrating how non-linear evolution is.
pnyikos
> pnyikos wrote:
> > On Sep 12, 8:02 pm, Stanley Friesen <sar...@friesen.net> wrote:
> >> pnyikos <nyik...@bellsouth.net> wrote:
> >>> On Sep 1, 11:40 am, John Harshman <jharsh...@pacbell.net> wrote:
> >>>> [snip snip]
> >>>> Not a sequence, but a branching tree. You can only turn it into a
> >>>> sequence by supposing there's a "main line" and "side branches".
> >>> Now it's my turn to be puzzled: don't they talk about the "horse
> >>> sequence" from *Hyracotherium* to *Equus* while ignorig the "side
> >>> branches," even though a case could be made for the "main line" ending
> >>> in *Hypohippus*?
> >> This is said by some, mostly in popular works, but it is incorrect. The
> >> actual evolution of the equine clade is very, very bushy.
>
> > Yes, I know. But I think "the horse sequence" ought to refer to a
> > chain of animals that threads its way through the bush, just like a
> > tree climber climbing out onto a limb and then a thick branch without
> > going any further up the trunk nor the main part of the limb.
>
> Please define "main part of the limb" and "trunk" in the current context.
to browsers with low-crowned teeth and three fairly big toes, like
Hypohippus, while the main part of the limb on which Equus sits goes
to *Hipparion* and other species which are conservative in retaining
the side toes with hooves (as opposed to mere splints).
I admit this is not a scientific definition, but it seems to put a bit
of order into the discussion.
> > In fact, this chain even threads its way up to the species that we
> > call "horse" as opposed to "donkey, ..." in the popular accounts, but
> > they almost never mention the species name.
>
> Because they're all Equus and not all that different from each other as
> horses go.
> Of course we have no such chain unless you can assign actual
> ancestry.
creationists. So the chain exists. And we have a darn good idea of
what the best approximation to that chain is among the species known
from fossils.
Some regulars of sci.bio.paleontology in the 1990's insisted it would
be *wrong* to assign scientific names (genus and species) to the last
common ancestors of various taxa, like the last common ancestor of all
the extant mammals, simply because it would be impossible to ever be
sure we had a fossil of that LCA. Do you agree with them?
If not, then scientists could give names to the LCA of, say, Equus and
Mesohippus, and then tell how much its fossils would differ from what
we have of Mesohippus fossils; perhaps not at all.
> >> It is just
> >> that only one small remnant - the genus Equus - survives, so
> >> popularizers can make a good show of imagining that the modern horse was
> >> the "main line".
>
> > That's a purely subjective use of "main line". It even leaves asses
> > and zebras out in the cold.
>
> What genus do you think asses and zebras belong to, just out of curiosity?
not to the genus Equus.
Equus asinus is the common donkey. There are three kinds of zebras
and I don't even know whether they belong to the same species. In
fact, for all know, the informal group "zebra" may be polyphyletic.
This reminds me of the old riddle, "Is the zebra a white animal with
black stripes or a black animal with white stripes?" Leaving aside
such smart-alecky answers as "Neither. It is either a light brown
animal with dark brown stripes or a dark brown animal with light brown
stripes," it seems to boil down to the question of what the undercoat
of the zebra is like.
And the opinion on this is divided in the places where I have read
answers to this riddle. It may even depend on the variety
(subspecies? species?) of zebra.
A sign of the sad state to which Usenet has sunk is that there is no
such group as sci.bio.zoology, and sci.bio is only available as an
archive. So we seem to have to fall back on the groups to which this
is crossposted for answers.
Peter Nyikos
John Harshman
reason for declaring the most conservative lineages to be either a "main
part" or a "trunk"; those terms imply something quite different, and
something that in fact doesn't exist.
> I admit this is not a scientific definition, but it seems to put a bit
> of order into the discussion.
attached to those terms, but only by denying any connection to their
typical meanings. Better to come up with a new term that has no baggage.
How about "conservative lineages"? The next question is what use it is
to have a term for conservative lineages, which must at any rate be a
subjective assessment, as most lineages will be derived in some ways and
primitive in others. Are humans, retaining 5 toes, more conservative
than horses, or are we more derived in being bipedal with big brains?
>>> In fact, this chain even threads its way up to the species that we
>>> call "horse" as opposed to "donkey, ..." in the popular accounts, but
>>> they almost never mention the species name.
>> Because they're all Equus and not all that different from each other as
>> horses go.
>
> Tell that to someone who tries to breed a pair of mules.
interbreed, you might have a point.
>> Of course we have no such chain unless you can assign actual
>> ancestry.
>
> Ancestry exists all the way down, unless you want to really cater to
> creationists. So the chain exists. And we have a darn good idea of
> what the best approximation to that chain is among the species known
> from fossils.
almost nil. So what's the point?
> Some regulars of sci.bio.paleontology in the 1990's insisted it would
> be *wrong* to assign scientific names (genus and species) to the last
> common ancestors of various taxa, like the last common ancestor of all
> the extant mammals, simply because it would be impossible to ever be
> sure we had a fossil of that LCA. Do you agree with them?
then yes. If you're talking about assigning names to actual fossils,
then no. But of course we can't say that any actual fossils are
ancestral, so the question would seem never to come up.
> If not, then scientists could give names to the LCA of, say, Equus and
> Mesohippus, and then tell how much its fossils would differ from what
> we have of Mesohippus fossils; perhaps not at all.
>>>> It is just
>>>> that only one small remnant - the genus Equus - survives, so
>>>> popularizers can make a good show of imagining that the modern horse was
>>>> the "main line".
>>> That's a purely subjective use of "main line". It even leaves asses
>>> and zebras out in the cold.
>> What genus do you think asses and zebras belong to, just out of curiosity?
>
> Equus, of course. I was referring to the label "the modern horse" and
> not to the genus Equus.
intention of the author.
Ernest Major
<jhar...@pacbell.net> writes
>> Mesohippus, and then tell how much its fossils would differ from what
>> we have of Mesohippus fossils; perhaps not at all.
>
>I see no reason to name a hypothetical animal.
Consequently it is not possible to formally give a species name to a
hypothetical plant or animal. (The bacterial code, IIRC, requires a
deposited culture - a problem which is worked round with Candidatus
status.)
--
alias Ernest Major
John Harshman
> In message <LJudnRsDZu2...@giganews.com>, John Harshman
> <jhar...@pacbell.net> writes
>>> If not, then scientists could give names to the LCA of, say, Equus and
>>> Mesohippus, and then tell how much its fossils would differ from what
>>> we have of Mesohippus fossils; perhaps not at all.
>>
>> I see no reason to name a hypothetical animal.
>
> Both the ICBN and ICZN requires that species have a designated type.
> Consequently it is not possible to formally give a species name to a
> hypothetical plant or animal.
> (The bacterial code, IIRC, requires a
> deposited culture - a problem which is worked round with Candidatus
> status.)
pnyikos
> In message <LJudnRsDZu2p-ufT4p2d...@giganews.com>, John Harshman
> <jharsh...@pacbell.net> writes
> >> If not, then scientists could give names to the LCA of, say, Equus and
> >> Mesohippus, and then tell how much its fossils would differ from what
> >> we have of Mesohippus fossils; perhaps not at all.
>
> >I see no reason to name a hypothetical animal.
>
> Both the ICBN and ICZN requires that species have a designated type.
> Consequently it is not possible to formally give a species name to a
> hypothetical plant or animal.
have a lot of fun with it.
Peter Nyikos
pnyikos
> pnyikos wrote:
> > On Sep 14, 12:44 am, John Harshman <jharsh...@pacbell.net> wrote:
> >> pnyikos wrote:
> >>> I think "the horse sequence" ought to refer to a
> >>> chain of animals that threads its way through the bush, just like a
> >>> tree climber climbing out onto a limb and then a thick branch without
> >>> going any further up the trunk nor the main part of the limb.
>
> >> Please define "main part of the limb" and "trunk" in the current context.
>
> > The part which changes least in the gross morphology. The trunk leads
> > to browsers with low-crowned teeth and three fairly big toes, like
> > Hypohippus, while the main part of the limb on which Equus sits goes
>
> While that's certainly a clear definition, I don't see any rational
> reason for declaring the most conservative lineages to be either a "main
> part" or a "trunk"; those terms imply something quite different, and
> something that in fact doesn't exist.
>
> > I admit this is not a scientific definition, but it seems to put a bit
> > of order into the discussion.
>
> Pointless order, I'm afraid. It's a definition that can be arbitrarily
> attached to those terms, but only by denying any connection to their
> typical meanings. Better to come up with a new term that has no baggage.
> How about "conservative lineages"?
quantify things, otherwise you could measure how close a complete
skeleton is to that of the LCA of two animals.
> The next question is what use it is
> to have a term for conservative lineages, which must at any rate be a
> subjective assessment, as most lineages will be derived in some ways and
> primitive in others. Are humans, retaining 5 toes, more conservative
> than horses, or are we more derived in being bipedal with big brains?
than the horse?
> >>> In fact, this chain even threads its way up to the species that we
> >>> call "horse" as opposed to "donkey, ..." in the popular accounts, but
> >>> they almost never mention the species name.
> >> Because they're all Equus and not all that different from each other as
> >> horses go.
>
> > Tell that to someone who tries to breed a pair of mules.
>
> If our sole criterion for "all that different" were indeed ability to
> interbreed, you might have a point.
>
> >> Of course we have no such chain unless you can assign actual
> >> ancestry.
>
> > Ancestry exists all the way down, unless you want to really cater to
> > creationists. So the chain exists. And we have a darn good idea of
> > what the best approximation to that chain is among the species known
> > from fossils.
>
> We can approximate a chain. But the chance that we have a true chain is
> almost nil.
chances of a universe being as fine-tuned as ours is almost nil?
I could tell you, for instance, that among the ~10^500 kinds of
universes that are solutions to the Feynmann equations, only a tiny
fraction are suitable for life as ours (Hawking, who has made a long
study of this issue, has said so). But I can almost predict your
reaction:
"Unless you have some reason for thinking that the solutions are
equally likely, or even that the whole small fraction of solutions
suitable for life are less likely than all the rest, this statement
gives no traction I could use."
Some people I could name would give a harsher [excuse the pun] closing
clause, e.g. "you are just indulging in an argument from personal
incredulity" or "this is just the discredited god of the gaps
nonsense."
> > Some regulars of sci.bio.paleontology in the 1990's insisted it would
> > be *wrong* to assign scientific names (genus and species) to the last
> > common ancestors of various taxa, like the last common ancestor of all
> > the extant mammals, simply because it would be impossible to ever be
> > sure we had a fossil of that LCA. Do you agree with them?
[hey! we're getting back on topic here!] like "Breviparops," believed
by some to have been made by the longest dinosaur of which we have any
knowledge at all.
> If you're talking about assigning names to purely hypothetical entities,
> then yes.
more perfectly into the hands of the creationists.
[...]
> > Mesohippus, and then tell how much its fossils would differ from what
> > we have of Mesohippus fossils; perhaps not at all.
___ many times as conservative wrt this LCA than Equus is.
> I see no reason to name a hypothetical animal.
cherry-picked without letting go of one of your cherished opinions,
can you? [I seem to be big on puns this morning.]
Peter Nyikos
John Harshman
Well, you can do that in the context of the particular characters you
have assessed. You can easily quantify it. The problem is that the
choice of characters is not quite objective, nor is the choice of codings.
>> The next question is what use it is
>> to have a term for conservative lineages, which must at any rate be a
>> subjective assessment, as most lineages will be derived in some ways and
>> primitive in others. Are humans, retaining 5 toes, more conservative
>> than horses, or are we more derived in being bipedal with big brains?
>
> Would you even say that the ring-tailed lemur is more conservative
> than the horse?
I wouldn't, but I wouldn't say it isn't either. How about you?
>>>>> In fact, this chain even threads its way up to the species that we
>>>>> call "horse" as opposed to "donkey, ..." in the popular accounts, but
>>>>> they almost never mention the species name.
>>>> Because they're all Equus and not all that different from each other as
>>>> horses go.
>>> Tell that to someone who tries to breed a pair of mules.
>> If our sole criterion for "all that different" were indeed ability to
>> interbreed, you might have a point.
>>
>>>> Of course we have no such chain unless you can assign actual
>>>> ancestry.
>>> Ancestry exists all the way down, unless you want to really cater to
>>> creationists. So the chain exists. And we have a darn good idea of
>>> what the best approximation to that chain is among the species known
>>> from fossils.
>> We can approximate a chain. But the chance that we have a true chain is
>> almost nil.
>
> Oh, really? Care to apply your reasoning to the claim that the
> chances of a universe being as fine-tuned as ours is almost nil?
No, since we have no basis for that. But my claim does have a basis. We
can at least come up with an estimate of the number of species that have
lived, and note that we have described only a tiny fraction of them. So
what's the probability that you have found an ancestor? You would have
to suppose that the fossil record is highly biased in favor of ancestors
in order to allow any reasonable chance.
> I could tell you, for instance, that among the ~10^500 kinds of
> universes that are solutions to the Feynmann equations, only a tiny
> fraction are suitable for life as ours (Hawking, who has made a long
> study of this issue, has said so). But I can almost predict your
> reaction:
>
> "Unless you have some reason for thinking that the solutions are
> equally likely, or even that the whole small fraction of solutions
> suitable for life are less likely than all the rest, this statement
> gives no traction I could use."
>
> Some people I could name would give a harsher [excuse the pun] closing
> clause, e.g. "you are just indulging in an argument from personal
> incredulity" or "this is just the discredited god of the gaps
> nonsense."
Thanks. From now on should I just let you carry on both sides of the
conversation? How would you defend yourself against that hypothetical
attack?
>>> Some regulars of sci.bio.paleontology in the 1990's insisted it would
>>> be *wrong* to assign scientific names (genus and species) to the last
>>> common ancestors of various taxa, like the last common ancestor of all
>>> the extant mammals, simply because it would be impossible to ever be
>>> sure we had a fossil of that LCA. Do you agree with them?
>
> I don't think they had any trouble with names assigned to trackways
> [hey! we're getting back on topic here!] like "Breviparops," believed
> by some to have been made by the longest dinosaur of which we have any
> knowledge at all.
Rightly so. Trackways aren't hypothetical. Ichnofossils need names just
like any other fossils.
>> If you're talking about assigning names to purely hypothetical entities,
>> then yes.
>
> "purely hypothetical"-- I can hardly imagine a formulation that plays
> more perfectly into the hands of the creationists.
Your imagination is a problem for you, but not for anyone else. Your
imaginings of what would or would not play into the hands of
creationists are of no great interest to me.
> [...]
>>> If not, then scientists could give names to the LCA of, say, Equus and
>>> Mesohippus, and then tell how much its fossils would differ from what
>>> we have of Mesohippus fossils; perhaps not at all.
>
> Now if we had some measure of things, we could say that Mesohippus is
> ___ many times as conservative wrt this LCA than Equus is.
>
>> I see no reason to name a hypothetical animal.
>
> The creationists would love this one. And you can't even say it was
> cherry-picked without letting go of one of your cherished opinions,
> can you? [I seem to be big on puns this morning.]
You should give up the puns, since you're very bad at it. And at
reasoning, apparently. But let me make clear that this, like the other
notions you have that I'm giving some gift to creationists, is in your
imagination only.
Are you in fact proposing that we assign scientific names to
hypothetical organisms?
pnyikos
> pnyikos wrote:
> > On Sep 21, 6:37 pm, John Harshman <jharsh...@pacbell.net> wrote:
> >> pnyikos wrote:
> >>> On Sep 14, 12:44 am, John Harshman <jharsh...@pacbell.net> wrote:
> >> The next question is what use it is
> >> to have a term for conservative lineages, which must at any rate be a
> >> subjective assessment, as most lineages will be derived in some ways and
> >> primitive in others. Are humans, retaining 5 toes, more conservative
> >> than horses, or are we more derived in being bipedal with big brains?
>
> > Would you even say that the ring-tailed lemur is more conservative
> > than the horse?
>
> I wouldn't, but I wouldn't say it isn't either. How about you?
"Virginia" opossum *Didelphis* is more conservative than the red
kangaroo *Macropus*.
That's partly because I have Edwin Colbert's word that *Didelphis* is
a "living fossil" and "a Cretaceous mammal". [_The Evolution of the
Vertebrates_]. But the real reason is the justifications he gives for
that.
> >>>>> [pnyikos:]In fact, this chain even threads its way up to the species
> >>>>> accounts, but they almost never mention the species name.
>
> >>>> Because they're all Equus and not all that different from each other as
> >>>> horses go.
>
> >>> Tell that to someone who tries to breed a pair of mules.
> >> If our sole criterion for "all that different" were indeed ability to
> >> interbreed, you might have a point.
that you consider to be objective: the concept of species. Otherwise,
the way you write, someone might think that you have no "objective"
criteria for saying members of different species in the same genus are
more similar than members of different phyla.
> >>>> Of course we have no such chain unless you can assign actual
> >>>> ancestry.
> >>> Ancestry exists all the way down, unless you want to really cater to
> >>> creationists. So the chain exists. And we have a darn good idea of
> >>> what the best approximation to that chain is among the species known
> >>> from fossils.
> >> We can approximate a chain. But the chance that we have a true chain is
> >> almost nil.
>
> > Oh, really? Care to apply your reasoning to the claim that the
> > chances of a universe being as fine-tuned as ours is almost nil?
>
> No, since we have no basis for that.
the cladophile arguments for "almost nil".
>But my claim does have a basis. We
> can at least come up with an estimate of the number of species that have
> lived, and note that we have described only a tiny fraction of them. So
> what's the probability that you have found an ancestor?
about fine tuniing. Surely you have better reasons than this puerile
claim for saying "almost nil".
> You would have
> to suppose that the fossil record is highly biased in favor of ancestors
> in order to allow any reasonable chance.
horse, we have lots of fossils of *Hyracotherium*, *Orohippus* and
*Epihippus*. I'd say the probability that at least one of them is a
direct ancestor of *Mesohippus* is very good. AFAIK, there is not a
single character in any of them that would shed doubt on this.
And here is another consideration, in the form of an analogy. The
first three genera resemble each other a lot more than any two genera
of living antelopes, no? It is even generally hypothesized that they
were in a direct line of descent from each other.
There are not all that many species of antelopes on the earth today;
are you reasonably confident that there were many other species around
that resembled *Mesohippus* more than any of the three I mentioned?
And even if there were, to say that the probability that any of the
three were ancestral to *Mesohiippus* was "almost nil" is a huge
stretch.
Mind you, I'm not saying that any of the *individuals* of whom we have
fossils is ancestral; all I'm suggesting is that they could have
interbred with a direct ancestor and had fertile offspring with it, or
at worst have produced the equivalent of mules and hinnies [is that
the plural of "hinny"?].
[Here I've deleted some comments of mine that evidently rubbed you the
wrong way, along with your reaction.]
> >>> Some regulars of sci.bio.paleontology in the 1990's insisted it would
> >>> be *wrong* to assign scientific names (genus and species) to the last
> >>> common ancestors of various taxa, like the last common ancestor of all
> >>> the extant mammals, simply because it would be impossible to ever be
> >>> sure we had a fossil of that LCA. Do you agree with them?
>
> > I don't think they had any trouble with names assigned to trackways
> > [hey! we're getting back on topic here!] like "Breviparops," believed
> > by some to have been made by the longest dinosaur of which we have any
> > knowledge at all.
>
> Rightly so. Trackways aren't hypothetical. Ichnofossils need names just
> like any other fossils.
Peter Nyikos
pnyikos
> pnyikos wrote:
> > On Sep 21, 6:37 pm, John Harshman <jharsh...@pacbell.net> wrote:
> >> If you're talking about assigning names to purely hypothetical entities,
> >> then yes.
>
> > "purely hypothetical"-- I can hardly imagine a formulation that plays
> > more perfectly into the hands of the creationists.
>
> Your imagination is a problem for you, but not for anyone else. Your
> imaginings of what would or would not play into the hands of
> creationists are of no great interest to me.
MORE perfectly into their hands?
> > [...]
> >>>[pnyikos:] scientists could give names to the LCA of, say, Equus and
> >>> we have of Mesohippus fossils; perhaps not at all.
>
> > The creationists would love this one. And you can't even say it was
> > cherry-picked without letting go of one of your cherished opinions,
> > can you? [I seem to be big on puns this morning.]
>
> You should give up the puns, since you're very bad at it.
> And at
> reasoning, apparently. But let me make clear that this, like the other
> notions you have that I'm giving some gift to creationists, is in your
> imagination only.
>
> Are you in fact proposing that we assign scientific names to
> hypothetical organisms?
terminology makes it sould like you've given up on the idea that there
ever were such things as last common ancestors [LCA].
Peter Nyikos
John Harshman
> On Sep 22, 12:21 pm, John Harshman <jharsh...@pacbell.net> wrote:
>> pnyikos wrote:
>>> On Sep 21, 6:37 pm, John Harshman <jharsh...@pacbell.net> wrote:
>>>> pnyikos wrote:
>>>>> On Sep 14, 12:44 am, John Harshman <jharsh...@pacbell.net> wrote:
>
>>>> The next question is what use it is
>>>> to have a term for conservative lineages, which must at any rate be a
>>>> subjective assessment, as most lineages will be derived in some ways and
>>>> primitive in others. Are humans, retaining 5 toes, more conservative
>>>> than horses, or are we more derived in being bipedal with big brains?
>>> Would you even say that the ring-tailed lemur is more conservative
>>> than the horse?
>> I wouldn't, but I wouldn't say it isn't either. How about you?
>
> I'd have to think about it. But I would already say that the
> "Virginia" opossum *Didelphis* is more conservative than the red
> kangaroo *Macropus*.
>
> That's partly because I have Edwin Colbert's word that *Didelphis* is
> a "living fossil" and "a Cretaceous mammal". [_The Evolution of the
> Vertebrates_]. But the real reason is the justifications he gives for
> that.
Which is? Certainly I would agree with that impression, though I doubt
the average Cretaceous mammal had a prehensile tail.
>>>>>>> [pnyikos:]In fact, this chain even threads its way up to the species
>>>>>>> that we call "horse" as opposed to "donkey, ..." in the popular
>>>>>>> accounts, but they almost never mention the species name.
>>>>>> Because they're all Equus and not all that different from each other as
>>>>>> horses go.
>>>>> Tell that to someone who tries to breed a pair of mules.
>>>> If our sole criterion for "all that different" were indeed ability to
>>>> interbreed, you might have a point.
>
> Well, it harks back to the ONLY level in the Linnean classification
> that you consider to be objective: the concept of species. Otherwise,
> the way you write, someone might think that you have no "objective"
> criteria for saying members of different species in the same genus are
> more similar than members of different phyla.
I'm not seeing any connection between your first and second sentences.
Have you lost sight of any point you are trying to make here?
>>>>>> Of course we have no such chain unless you can assign actual
>>>>>> ancestry.
>>>>> Ancestry exists all the way down, unless you want to really cater to
>>>>> creationists. So the chain exists. And we have a darn good idea of
>>>>> what the best approximation to that chain is among the species known
>>>>> from fossils.
>>>> We can approximate a chain. But the chance that we have a true chain is
>>>> almost nil.
>>> Oh, really? Care to apply your reasoning to the claim that the
>>> chances of a universe being as fine-tuned as ours is almost nil?
>> No, since we have no basis for that.
>
> We have some, but you just aren't as familiar with it as you are with
> the cladophile arguments for "almost nil".
Feel free to enlighten me. In fact, I have for some time been asking
you, without much success, to present your argument.
>> But my claim does have a basis. We
>> can at least come up with an estimate of the number of species that have
>> lived, and note that we have described only a tiny fraction of them. So
>> what's the probability that you have found an ancestor?
>
> This line of argument seems to be reverse-engineered from your mantras
> about fine tuniing. Surely you have better reasons than this puerile
> claim for saying "almost nil".
What is puerile (or, better, wrong) about my claim?
>> You would have
>> to suppose that the fossil record is highly biased in favor of ancestors
>> in order to allow any reasonable chance.
>
> You have to approach this on a case by case basis. In the case of the
> horse, we have lots of fossils of *Hyracotherium*, *Orohippus* and
> *Epihippus*. I'd say the probability that at least one of them is a
> direct ancestor of *Mesohippus* is very good. AFAIK, there is not a
> single character in any of them that would shed doubt on this.
How did you estimate that probability?
> And here is another consideration, in the form of an analogy. The
> first three genera resemble each other a lot more than any two genera
> of living antelopes, no?
I don't know. Make your case for that assertion.
> It is even generally hypothesized that they
> were in a direct line of descent from each other.
Hypothesized by whom?
> There are not all that many species of antelopes on the earth today;
> are you reasonably confident that there were many other species around
> that resembled *Mesohippus* more than any of the three I mentioned?
Here we encounter the difficulty of identifying species in the fossil
record. How many species are bundled into Mesohippus? I have no idea.
But is it your claim that we have sampled every species of equid that
was living at that time?
> And even if there were, to say that the probability that any of the
> three were ancestral to *Mesohiippus* was "almost nil" is a huge
> stretch.
>
> Mind you, I'm not saying that any of the *individuals* of whom we have
> fossils is ancestral; all I'm suggesting is that they could have
> interbred with a direct ancestor and had fertile offspring with it, or
> at worst have produced the equivalent of mules and hinnies [is that
> the plural of "hinny"?].
I don't see any way to test your claim. Do you?
John Harshman
> On Sep 22, 12:21 pm, John Harshman <jharsh...@pacbell.net> wrote:
>> pnyikos wrote:
>>> On Sep 21, 6:37 pm, John Harshman <jharsh...@pacbell.net> wrote:
>
>>>> If you're talking about assigning names to purely hypothetical entities,
>>>> then yes.
>>> "purely hypothetical"-- I can hardly imagine a formulation that plays
>>> more perfectly into the hands of the creationists.
>> Your imagination is a problem for you, but not for anyone else. Your
>> imaginings of what would or would not play into the hands of
>> creationists are of no great interest to me.
>
> Can you think of anything written by an "evolutionist" that would play
> MORE perfectly into their hands?
of greater perfection. Gould's "trade secret of paleontology" is the one
that first comes to mind. Whether one could be quote-mined is hardly an
important consideration. Better to ask whether what I say is true.
>>> [...]
>>>>> [pnyikos:] scientists could give names to the LCA of, say, Equus and
>>>>> Mesohippus, and then tell how much its fossils would differ from what
>>>>> we have of Mesohippus fossils; perhaps not at all.
> [...]
>>>> I see no reason to name a hypothetical animal.
>>> The creationists would love this one. And you can't even say it was
>>> cherry-picked without letting go of one of your cherished opinions,
>>> can you? [I seem to be big on puns this morning.]
>> You should give up the puns, since you're very bad at it.
>
> Sour grapes?
>> And at
>> reasoning, apparently. But let me make clear that this, like the other
>> notions you have that I'm giving some gift to creationists, is in your
>> imagination only.
>>
>> Are you in fact proposing that we assign scientific names to
>> hypothetical organisms?
>
> I'm proposing that we assign them to very REAL organisms. Your
> terminology makes it sould like you've given up on the idea that there
> ever were such things as last common ancestors [LCA].
existed. Your idea that ancestors don't exist unless we name them is
silly. And practically speaking, what would the type specimen be? How
would we decide whether a future discovery is referrable to that name?
pnyikos
> pnyikos wrote:
> > On Sep 22, 12:21 pm, John Harshman <jharsh...@pacbell.net> wrote:
> >> pnyikos wrote:
> >>> On Sep 21, 6:37 pm, John Harshman <jharsh...@pacbell.net> wrote:
>
> >>>> If you're talking about assigning names to purely hypothetical entities,
> >>>> then yes.
> >>> "purely hypothetical"-- I can hardly imagine a formulation that plays
> >>> more perfectly into the hands of the creationists.
> >> Your imagination is a problem for you, but not for anyone else. Your
> >> imaginings of what would or would not play into the hands of
> >> creationists are of no great interest to me.
>
> > Can you think of anything written by an "evolutionist" that would play
> > MORE perfectly into their hands?
>
> I suppose one could consider any of the many habitual quote-mines to be
> of greater perfection. Gould's "trade secret of paleontology" is the one
> that first comes to mind.
taxa at the nodes, but does not commit the solecism of saying that the
nodes represent "purely hypothetical" entities.
[...]
> >> Are you in fact proposing that we assign scientific names to
> >> hypothetical organisms?
>
> > I'm proposing that we assign them to very REAL organisms. Your
> > terminology makes it sould like you've given up on the idea that there
> > ever were such things as last common ancestors [LCA].
>
> Any organism we have not found can't be real to us, even if it must have
> existed. Your idea that ancestors don't exist unless we name them is
> silly.
have. Try not to stray from the point, which was the literal meaning
of "purely hypothetical".
> And practically speaking, what would the type specimen be?
> How
> would we decide whether a future discovery is referrable to that name?
it has all the characters that have been attributed to
______________. The [for now, anyway] unconventional name ___________
could be always put into quotes, like "Proavis".
Peter Nyikos
pnyikos
> pnyikos wrote:
> > On Sep 22, 12:21 pm, John Harshman <jharsh...@pacbell.net> wrote:
> >> pnyikos wrote:
> >>> On Sep 21, 6:37 pm, John Harshman <jharsh...@pacbell.net> wrote:
> >>>> I see no reason to name a hypothetical animal.
> >>> The creationists would love this one. And you can't even say it was
> >>> cherry-picked without letting go of one of your cherished opinions,
> >>> can you? [I seem to be big on puns this morning.]
> >> You should give up the puns, since you're very bad at it.
>
> > Sour grapes?
>
> Very bad at it.
instances.
> >> And at
> >> reasoning, apparently.
The irony is priceless. And that's even without the following
documentation.
_______________begin repost of a reply to me____________
Newsgroups: soc.history.medieval
From: mike.d...@NOSPAMboeing.com (Mike Dana)
Date: Fri, 09 Feb 2001 00:45:16 GMT
Local: Thurs, Feb 8 2001 8:45 pm
Subject: Re: The Goose And God [Was: Below-50-IQ...]
On 8 Feb 2001 17:40:59 GMT, nyi...@math.sc.edu (Peter Nyikos) wrote:
>I'll be on posting break tomorrow and the rest of the weekend,
>so this t.g.i.f. post comes now instead.
>mike.d...@NOSPAMboeing.com (Mike Dana) writes:
>[snip enormous expense caused by Debono, Gans, and Renia
>to people who pay for internet access by the minute] ;-)
>>You *do* realize, don't you, that Diaperfanny is a minor sept of the
>>Diaperhead Clan, [...]
>Not a minor oct?
>Not even an octave in C minor?
>Nor a minor sex?
>Nor...but I'd better stop here.
>>--The Punstrel
>Peter Nyikos -- standard disclaimer --
Bravo! Nicely twisted; from Scottish (sorta) Clans, to Roman numbers,
to music, to almost-but-not-quite-a-suggestion of a statutory offence!
There *is* a sense of humor hiding in there! :-D
--The Punstrel
================ post archived
at http://groups.google.com/group/soc.history.medieval/msg/0d528b7e6d518d39
Message-ID: <3a833c26...@news.gte.net>
Eat your heart out, John: the Punstrel was a well-known and generally
liked specialist on puns in soc.history.medieval, one of Gans's
stomping grounds.
And I even got an accolade from an adversary of mine for the above
performance:
"I was going to say SOHF (sense of humour failure) But by
all the Gods that are Holy you ade me smile Peter! *gosh*"
http://groups.google.com/group/soc.history.medieval/msg/c5d17a8ec5dc54b9
Message-ID: <aes58tksussm3qnjh...@4ax.com>
Peter Nyikos
John Harshman
> On Sep 29, 10:59 am, John Harshman <jharsh...@pacbell.net> wrote:
>> pnyikos wrote:
>>> On Sep 22, 12:21 pm, John Harshman <jharsh...@pacbell.net> wrote:
>>>> pnyikos wrote:
>>>>> On Sep 21, 6:37 pm, John Harshman <jharsh...@pacbell.net> wrote:
>>>>>> If you're talking about assigning names to purely hypothetical entities,
>>>>>> then yes.
>>>>> "purely hypothetical"-- I can hardly imagine a formulation that plays
>>>>> more perfectly into the hands of the creationists.
>>>> Your imagination is a problem for you, but not for anyone else. Your
>>>> imaginings of what would or would not play into the hands of
>>>> creationists are of no great interest to me.
>>> Can you think of anything written by an "evolutionist" that would play
>>> MORE perfectly into their hands?
>> I suppose one could consider any of the many habitual quote-mines to be
>> of greater perfection. Gould's "trade secret of paleontology" is the one
>> that first comes to mind.
>
> That doesn't even come close. It says that our trees don't have any
> taxa at the nodes, but does not commit the solecism of saying that the
> nodes represent "purely hypothetical" entities.
representatives is in fact hypothetical. I don't know what else it would
be. Hypothetical doesn't imply nonexistent.
>>>> Are you in fact proposing that we assign scientific names to
>>>> hypothetical organisms?
>>> I'm proposing that we assign them to very REAL organisms. Your
>>> terminology makes it sould like you've given up on the idea that there
>>> ever were such things as last common ancestors [LCA].
>> Any organism we have not found can't be real to us, even if it must have
>> existed. Your idea that ancestors don't exist unless we name them is
>> silly.
>
> It isn't my idea, turkey. It isn't even an idea a creationist would
> have. Try not to stray from the point, which was the literal meaning
> of "purely hypothetical".
no actual exemplars.
>> And practically speaking, what would the type specimen be?
>
> Nitpick based on a quaint custom of biologists.
hasten to add, in comparison with the average person. Just in comparison
with biologists. Naming hypotheticals leads to real problems.
>> How
>> would we decide whether a future discovery is referrable to that name?
>
> No need to decide, just to mention in the course of a description that
> it has all the characters that have been attributed to
> ______________. The [for now, anyway] unconventional name ___________
> could be always put into quotes, like "Proavis".
John Harshman
> On Sep 29, 10:59 am, John Harshman <jharsh...@pacbell.net> wrote:
>> pnyikos wrote:
>>> On Sep 22, 12:21 pm, John Harshman <jharsh...@pacbell.net> wrote:
>>>> pnyikos wrote:
>>>>> On Sep 21, 6:37 pm, John Harshman <jharsh...@pacbell.net> wrote:
>
>
>>>>>> I see no reason to name a hypothetical animal.
>>>>> The creationists would love this one. And you can't even say it was
>>>>> cherry-picked without letting go of one of your cherished opinions,
>>>>> can you? [I seem to be big on puns this morning.]
>
>>>> You should give up the puns, since you're very bad at it.
>>> Sour grapes?
>> Very bad at it.
>
> You are very bad at reasoning, making this claim based on two
> instances.
defending your sense of humor?
pnyikos
Martinez on this score; see my parting shot below.
> >>>> Are you in fact proposing that we assign scientific names to
> >>>> hypothetical organisms?
> >>> I'm proposing that we assign them to very REAL organisms. Your
> >>> terminology makes it sould like you've given up on the idea that there
> >>> ever were such things as last common ancestors [LCA].
> >> Any organism we have not found can't be real to us, even if it must have
> >> existed. Your idea that ancestors don't exist unless we name them is
> >> silly.
>
> > It isn't my idea, turkey. It isn't even an idea a creationist would
> > have. Try not to stray from the point, which was the literal meaning
> > of "purely hypothetical".
>
> What do you think the literal meaning is? I think it means that we have
> no actual exemplars.
> >> And practically speaking, what would the type specimen be?
>
> > Nitpick based on a quaint custom of biologists.
>
> There is a fine example of your comparative ignorance of biology.
related customs that I call it quaint. J.L.B. Smith says a good bit
about them in _The Search Beneath the Sea_.
> Not, I
> hasten to add, in comparison with the average person. Just in comparison
> with biologists. Naming hypotheticals leads to real problems.
> >> How
> >> would we decide whether a future discovery is referrable to that name?
>
> > No need to decide, just to mention in the course of a description that
> > it has all the characters that have been attributed to
> > ______________. The [for now, anyway] unconventional name ___________
> > could be always put into quotes, like "Proavis".
>
> What is the value in doing this?
Martinez in on this running argument, and to let the chips fall where
they may. See:
http://groups.google.com/group/talk.origins/msg/971b05615e83ee54
Peter Nyikos
pnyikos
> pnyikos wrote:
> > On Sep 29, 10:59 am, John Harshman <jharsh...@pacbell.net> wrote:
> >> pnyikos wrote:
> >>> On Sep 22, 12:21 pm, John Harshman <jharsh...@pacbell.net> wrote:
> >>>> pnyikos wrote:
> >>>>> On Sep 21, 6:37 pm, John Harshman <jharsh...@pacbell.net> wrote:
>
> >>>>>> I see no reason to name a hypothetical animal.
> >>>>> The creationists would love this one. And you can't even say it was
> >>>>> cherry-picked without letting go of one of your cherished opinions,
> >>>>> can you? [I seem to be big on puns this morning.]
>
> >>>> You should give up the puns, since you're very bad at it.
> >>> Sour grapes?
> >> Very bad at it.
>
> > You are very bad at reasoning, making this claim based on two
> > instances.
>
> You are very bad at letting anything go.
you. You are simply one of the few people in talk.origins who can
have an extended debate with me without resorting to blatant
dishonesty.
> > Eat your heart out, John: the Punstrel was a well-known and generally
> > liked specialist on puns in soc.history.medieval, one of Gans's
> > stomping grounds.
>
> > And I even got an accolade from an adversary of mine for the above
> > performance:
>
> > "I was going to say SOHF (sense of humour failure) But by
> > all the Gods that are Holy you ade me smile Peter! *gosh*"
>
> >http://groups.google.com/group/soc.history.medieval/msg/c5d17a8ec5dc54b9
> Do you see the humor in your complete lack of humor in doggedly
> defending your sense of humor?
atmosphere in talk.origins. Fortunately, soc.history.medieval was
less influenced [although Gans did his best to make it political in
the broad Aristotelian sense fo the term] and people there could
afford to let some of their true opinions show where adversaries were
concerned.
Not that I think of you as an adversary; I reserve that term for
scoundrels like Paul Gans and Ron Okimoto. You have simply been
steeped for decades in the atmosphere that they create, so that you
don't realize how artificial your behavior is where things like humor
are concerned.
I should add, by the way, that I may have been hasty in concluding
that Debono was an adversary of mine; I got that impression from my
dig at the beginning of the included post about him and my adversaries
Renia and Gans. I don't recall enough about Debono himself right now.
Yup, he is the "adversary" from whom I quoted that two-liner. And I
think he was so frank that he actually gave a true hint that he was
about to make a "political" comment ("SOHF") about my dig at him,
Renia, and Gans, but my subsequent pun disarmed him.
Peter Nyikos
John Harshman
>>>>>> Are you in fact proposing that we assign scientific names to
>>>>>> hypothetical organisms?
>>>>> I'm proposing that we assign them to very REAL organisms. Your
>>>>> terminology makes it sould like you've given up on the idea that there
>>>>> ever were such things as last common ancestors [LCA].
>>>> Any organism we have not found can't be real to us, even if it must have
>>>> existed. Your idea that ancestors don't exist unless we name them is
>>>> silly.
>>> It isn't my idea, turkey. It isn't even an idea a creationist would
>>> have. Try not to stray from the point, which was the literal meaning
>>> of "purely hypothetical".
>> What do you think the literal meaning is? I think it means that we have
>> no actual exemplars.
>
> "imaginary" is what I associate with the term.
example a hypothetical particle (or if by some chance I've missed some
news, it was until fairly recently). Is it imaginary?
>>>> And practically speaking, what would the type specimen be?
>>> Nitpick based on a quaint custom of biologists.
>> There is a fine example of your comparative ignorance of biology.
>
> What ignorance? It is because I know a lot about the custom and
> related customs that I call it quaint. J.L.B. Smith says a good bit
> about them in _The Search Beneath the Sea_.
>> Not, I
>> hasten to add, in comparison with the average person. Just in comparison
>> with biologists. Naming hypotheticals leads to real problems.
>
> You don't seem to make a good case for that below.
>>>> How
>>>> would we decide whether a future discovery is referrable to that name?
>>> No need to decide, just to mention in the course of a description that
>>> it has all the characters that have been attributed to
>>> ______________. The [for now, anyway] unconventional name ___________
>>> could be always put into quotes, like "Proavis".
>> What is the value in doing this?
>
> This post of yours was the last straw, John. I've decided to let Ray
> Martinez in on this running argument, and to let the chips fall where
> they may. See:
>
> http://groups.google.com/group/talk.origins/msg/971b05615e83ee54
people to post? All news to me.
Darwin123
> On Aug 31, 7:46 am, "Rolf" <rolf.aalb...@tele2.no> wrote:
>
>
>
>
>
>
>
>
> > John Harshman wrote:
> > > pnyikos wrote:
> > >>>>>> articles about what appear to be tetrapod trackways that predate
> > >>>>>> such well- known tranisitional fish fossils as those we have of
> > >>>>>> Eusthenopteron, Panderichthys, and Tiktaalik:
> > >>>>>>http://www.nature.com/nature/journal/v463/n7277/full/463040a.html
> > >>>>>>http://www.nature.com/nature/journal/v463/n7277/full/nature08623.html
>
> > >> an ideal transitional between Eusthenopteron and Panderichthys on the
> > >> one hand, and the tetrapods on the other.
> > >>http://chronicle.uchicago.edu/081023/tiktaalik.shtml
> > >> [...]
> > >>>>>> similarly big gap for the first birds vs Dromaesaurs, is that
> > >>>>>> Eusthenopteron, Panderichthys, and Tiktaalik are "relicts" from
> > >>>>>> an earlier era where very similar transitional forms exist.
> > >>>>>> trackways is not adequate to settle the first one:
> > >>>>>> 1. These tracks represent a parallel evolution of a "failed
> > >>>>>> experiment" in tetrapody.
> > >>>>>> "footprint" of "Thinopus".
> > >>>>>> 3. The trackway has been improperly dated.
> > >>>>>> Can anyone help decide between the above four possibilities, or
> > >>>>>> argue for yet others? "possibility zero" is the favored
> > >>>>>> explanation I gave above.
> > >>>>> All are conceivable explanations, though 2 and 3 seem unlikely
> > >>>>> unless you have some argument for either of them.
> > >>>> And I don't. The second article does what looks like a good job of
> > >>>> taking care of 3, and its case for 2. being false looks convincing.
> > >>>>> 0 seems best. Do you have a
> > >>>>> preference?
> > >>> The more detail we can see in the trackway, the less likely. Agreed?
>
> > >> Only if the details are very similar to those of prints of
> > >> *Acanthostega*, *Ichthyostega*, or other confirmed tetrapods.
>
> > > Yes.
>
> > >> the idea of making Tetrapoda the designation of a comparatively small
> > >> crown group based on extant species. Ahlberg is another, and so is
> > >> Jennifer A. Clack:
> > >> The author disagrees with the move to restrict
> > >>http://tolweb.org/Ichthyostega/15015
>
> > > Don't confuse "Tetrapoda" with "tetrapod". Clack is talking about the
> > > latter.
>
> > >>> the fact that we know of tetrapods but don't know of any ancient
> > >>> non-tetrapod walking fish is also some evidence. Would you agree?
>
> > >> If the tracks are different--and it looks to me that the authors are
> > >> than those of the fish that it represents the next step from on the
> > >> way to tetrapods. Why should these "relicts" show up in the order in
> > >> which they supposedly arose over ten million years earlier?
>
> > > Better question: why shouldn't they? We're talking about a handful of
> > > fossils, for which any order would be likely enough even if it were
> > > random.
>
> > >> Eusthenopteron types to tetrapods. I refer you not only to the
> > >> University of Chicago website above but also to the two seminal
> > >> articles on this theme:
> > >> (6 April 2006):
> > >>http://www.nature.com/nature/journal/v440/n7085/pdf/nature04639.pdf
> > >> (16 October 2008):
> > >>http://www.nature.com/nature/journal/v455/n7215/full/nature07189.html
>
> > > Yes, and dromaeosaurs are fine transitionals too despite being mostly
> > > much later than Archaeopteryx. So?
>
> > >> The authors of the main article don't do a very good job of meeting
> > >> that objection:
>
> > >> ...why do the elpistostegids appear before
> > >> tetrapods in the body fossil record in a manner
> > >> that neatly simulates a stratophylogenetic fit (Fig. 5)?
> > >> ...
> > >> If their first appearance as body fossils reflects
> > >> the time when they first colonized environments
> > >> with preservation potential, as seems likely, the
> > >> elpistostegids evidently arrived in advance of the
> > >> tetrapods. The reason was presumably ecological
> > >> but cannot be determined at present.
> > >>http://www.nature.com/nature/journal/v463/n7277/full/nature08623.html
>
> > >> Peter Nyikos
>
> > The coelecanth went extinct 65 million years ago, except it didn't. I still
> > remember reading about it in 1938 although I didn't understand it.
>
> > Rolf
>
> Wow, you are a real old-timer! I wasn't even born until eight years
> later.
>
> I did read about the second coelacanth three years after it was
> caught. One of my prized possessions is a book given to me on my 12th
> birthday by my late father, written by the discoverer, J.L.B. Smith,
> _The Search Beneath the Sea_ , about his 14-year long hunt for a good
> specimen. The first one was just skin and skull by the time he got to
> it.
>
> Anyway, since the coelacanth is not assumed to be close to the
> ancestry of any tetrapods, it's not the best analogy to the puzzle
> facing the track-discoverers.
The coelocanth is a lobe-finned fish, together with lungfish. All
lobe-finned fish are supposed to belong to a clade that includes the
tetrapods.
The problem you are discussing isn't so much which fossil
represents the most recent common ancestor (MRCA), but where did the
MRCA live. Deciding which fossil most resembles the MRCA is
equivalent to deciding what the MRCA looked like. You can't tell what
the MRCA looks like until you know where the MRCA lived.
The mainstream theory is that the tetrapods are a monophyletic
group. If this is true, then there is a most recent common ancestor
(MRCA) from which all the extant tetrapods are descended. However, the
mainstream still doesn't know where this MRCA lived.
The conventional wisdom (e.g., comic books) is that the MRCA of
tetrapods lived mostly on land. According to this view, the MRCA was
an amphibian whose life cycle vaguely resembled the life cycle of
today's amphibians. This means that juveniles lived in fresh water and
the adults lived on land.
Tiktaliik in this Conventional Wisdom view was probably not the
real MRCA because it couldn't live on land as an adult. It could have
been the ancestor of the MRCA, and is less likely to be the descendent
of the MRCA. If it was the ancestor of the MRCA, it is had descendents
that did not survive into today's world. Therefore, it shouldn't be
surprising that there were rather tetrapod looking creatures
coexisting wiht Tiktaalik.
If Tiktaliik was the descendent of the MRCA, then there are quite
possibly related species that looked more like tetrapods than
Tiktaliik. Again, it shouldn't be surprising that there are creatures
that look like tetrapods that coexist with Tiktallik.
Of course, it is quite possible that the conventional wisdom
(CW) is wrong. I think it is very likely that the MRCA lived full time
in fresh water, never going onto land even in adulthood. It had arms,
legs and lungs somewhat like a reptiles, but never came on land. It
used these arms and legs on the bottom of the river or lake it lived
in. It used its lungs occasionally when the water it lived in was
stagnant. Carp and catfish can breathe air when their water becomes
stagnate.
The MRCA may have even been an obligate air breather, the way many
fresh water fish are today. Not all fresh water fish that breathe air
live on land. The electric eel (not related to the tetrapods) can't
stay under water. The snake head also needs to breath air, but lives
in the water. There are actually lots of fresh water fish that need to
breath air but live all their lives under water. The MRCA may have
been among them.
In which case, Tikitalik may have been the MRCA. However, then the
CW is wrong. The first tetrapod was not terrestrial at any time in its
life. Then, it seems less likely that there would be coexisting
tetrapod-like creatures living with Tikitalik.
So the problem you are discussing isn't so much which fossil
represents the MRCA, but where did the MRCA live. If we knew where
the MRCA lived at various stages of its life, we would be able to
discuss the issue of fossil lineages better.
I don't see this as a fundamental problem, but I still hope it is
worked out in my lifetime. Where did the MRCA of all tetrapods live?
Did it live full time under fresh water (sticking its mouth out of the
water now and then)? Did it live part time in fresh water and its
adulthood on land? Did it have fully developed legs or just lobe fins?
Maybe the MRCA lived part time is salt water! There is no a priori
reason to expect the MRCA to be very similar to today's amphibians.
Maybe the amphibians are descended from a marine animal that adapted
to fresh water and then crawled on land sometime in the Jurassic!
In this case, it is quite possible that several land-dwelling animals
are descended from it. If distant relatives happen to already have the
arms, legs and lungs.
Forgive my spelling for Tiktaliik. I don't have a dictionary
handy !-)
>
> Peter Nyikos
John Harshman
>>>>> (Gauthier et al. 1989). In this page, the term
Not true at all. Most of what we know of ancestors must come from
comparing the features of their relatives (including but not limited to
their descendants). Parsimony is our chief guide. If the ancestor of
some group of species, for example, is embedded in a clade all of whose
known species are marine, we may reasonably conclude that the ancestor
was marine. We may in some cases be wrong, but that's the way to bet.
> The mainstream theory is that the tetrapods are a monophyletic
> group. If this is true, then there is a most recent common ancestor
> (MRCA) from which all the extant tetrapods are descended.
That's true regardless of whether they're monophyletic.
> However, the
> mainstream still doesn't know where this MRCA lived.
> The conventional wisdom (e.g., comic books) is that the MRCA of
> tetrapods lived mostly on land. According to this view, the MRCA was
> an amphibian whose life cycle vaguely resembled the life cycle of
> today's amphibians. This means that juveniles lived in fresh water and
> the adults lived on land.
The main problem here is confusion over what is meant by "tetrapod". If
we're going by extant species, i.e. the ancestor of crown group
Tetrapoda, then the inference is most probably correct. If you mean some
other group, the answer depends on what other group you mean. There
really is no way to tell from this post what you're talking about.
> Tiktaliik in this Conventional Wisdom view was probably not the
> real MRCA because it couldn't live on land as an adult. It could have
> been the ancestor of the MRCA, and is less likely to be the descendent
> of the MRCA. If it was the ancestor of the MRCA, it is had descendents
> that did not survive into today's world. Therefore, it shouldn't be
> surprising that there were rather tetrapod looking creatures
> coexisting wiht Tiktaalik.
> If Tiktaliik was the descendent of the MRCA, then there are quite
> possibly related species that looked more like tetrapods than
> Tiktaliik. Again, it shouldn't be surprising that there are creatures
> that look like tetrapods that coexist with Tiktallik.
Wow. How many ways can you spell Tiktaalik?
> Of course, it is quite possible that the conventional wisdom
> (CW) is wrong. I think it is very likely that the MRCA lived full time
> in fresh water, never going onto land even in adulthood.
The MRCA of what, exactly? Almost certainly not the MRCA of extant
tetrapods.
> It had arms,
> legs and lungs somewhat like a reptiles, but never came on land. It
> used these arms and legs on the bottom of the river or lake it lived
> in. It used its lungs occasionally when the water it lived in was
> stagnant. Carp and catfish can breathe air when their water becomes
> stagnate.
> The MRCA may have even been an obligate air breather, the way many
> fresh water fish are today. Not all fresh water fish that breathe air
> live on land. The electric eel (not related to the tetrapods) can't
> stay under water. The snake head also needs to breath air, but lives
> in the water. There are actually lots of fresh water fish that need to
> breath air but live all their lives under water. The MRCA may have
> been among them.
How would we tell whether this was true? Mostly by mapping characters
onto phylogenies. But you have it backwards. How it looked tells us
where it lived more often than the reverse.
> In which case, Tikitalik may have been the MRCA. However, then the
> CW is wrong. The first tetrapod was not terrestrial at any time in its
> life. Then, it seems less likely that there would be coexisting
> tetrapod-like creatures living with Tikitalik.
I don't see how any of that follows.
> So the problem you are discussing isn't so much which fossil
> represents the MRCA, but where did the MRCA live. If we knew where
> the MRCA lived at various stages of its life, we would be able to
> discuss the issue of fossil lineages better.
How would we determine this?
> I don't see this as a fundamental problem, but I still hope it is
> worked out in my lifetime. Where did the MRCA of all tetrapods live?
> Did it live full time under fresh water (sticking its mouth out of the
> water now and then)? Did it live part time in fresh water and its
> adulthood on land? Did it have fully developed legs or just lobe fins?
> Maybe the MRCA lived part time is salt water! There is no a priori
> reason to expect the MRCA to be very similar to today's amphibians.
> Maybe the amphibians are descended from a marine animal that adapted
> to fresh water and then crawled on land sometime in the Jurassic!
Very unlikely. There are Triassic frogs, if nothing else. Knowledge of
phylogeny really does help us. And certain adult structures would be
useless in the water, just as certain other such structures would be
useless on land. The question to ask is which structures the ancestor
had. (After we figure out what ancestor you're talking about.)
> In this case, it is quite possible that several land-dwelling animals
> are descended from it. If distant relatives happen to already have the
> arms, legs and lungs.
> Forgive my spelling for Tiktaliik. I don't have a dictionary
> handy !-)
Again, it's Tiktaalik. Don't need a dictionary, really. You have the web.
pnyikos
I was focused on a thread involving "Dr. Dr. Kleinman" most of that
time. I am still very short on time but I thought I'd revisit this
thread because it impinges directly on a successful prediction of
evolutionary theory. But how successful? Was the discovery of
Tiktaalik a stroke of undeserved luck?
CC to Harshman, because of the long delay in replying.
On Oct 10, 6:00 pm, John Harshman <jharsh...@pacbell.net> wrote:
> Darwin123 wrote:
> > On Aug 31, 11:08 am, pnyikos <nyik...@bellsouth.net> wrote:
> >> On Aug 31, 7:46 am, "Rolf" <rolf.aalb...@tele2.no> wrote:
>
> >>> John Harshman wrote:
> >>>> pnyikos wrote:
> >>>>> On Aug 29, 7:45 pm, John Harshman <jharsh...@pacbell.net> wrote:
> >>>>>> pnyikos wrote:
> >>>>>>> On Aug 29, 5:10 pm, John Harshman <jharsh...@pacbell.net> wrote:
> >>>>>>>> pnyikos wrote:
> >>>>>>>>> In the 7 January 2010 issue of _Nature_, there is a pair of
> >>>>>>>>> articles about what appear to be tetrapod trackways that predate
> >>>>>>>>> such well- known tranisitional fish fossils as those we have of
> >>>>>>>>> Eusthenopteron, Panderichthys, and Tiktaalik:
> >>>>>>>>>http://www.nature.com/nature/journal/v463/n7277/full/463040a.html
> >>>>>>>>>http://www.nature.com/nature/journal/v463/n7277/full/nature08623.html
years, then the expensive expedition to Ellesmere Island, where
Tiktaalik was found, was a big gamble, and not the good bet that it
seems to have been in hindsight.
> >>>>> Here is a very nice website on Tiktaalik, showing how it seems to be
> >>>>> an ideal transitional between Eusthenopteron and Panderichthys on the
> >>>>> one hand, and the tetrapods on the other.
> >>>>>http://chronicle.uchicago.edu/081023/tiktaalik.shtml
> >>>>> [...]
> >>>>>>>>> The favored explanation for the discrepancy, reminiscent of the
> >>>>>>>>> similarly big gap for the first birds vs Dromaesaurs, is that
> >>>>>>>>> Eusthenopteron, Panderichthys, and Tiktaalik are "relicts" from
> >>>>>>>>> an earlier era where very similar transitional forms exist.
> >>>>>>>>> But I can think of several others, and my interpretation of the
> >>>>>>>>> trackways is not adequate to settle the first one:
> >>>>>>>>> 1. These tracks represent a parallel evolution of a "failed
> >>>>>>>>> experiment" in tetrapody.
> >>>>>>>>> 2. The "tracks" are natural geological formations, like the
> >>>>>>>>> "footprint" of "Thinopus".
> >>>>>>>>> 3. The trackway has been improperly dated.
> >>>>>>>>> Can anyone help decide between the above four possibilities, or
> >>>>>>>>> argue for yet others? "possibility zero" is the favored
> >>>>>>>>> explanation I gave above.
> >>>>>>>> preference?
>
> >>>>>>> Mine is for 0 also, though 1. is an intriguing possibility.
>
> >>>>>> The more detail we can see in the trackway, the less likely. Agreed?
>
> >>>>> Only if the details are very similar to those of prints of
> >>>>> *Acanthostega*, *Ichthyostega*, or other confirmed tetrapods.
>
> >>>> Yes.
> >>>>> If the tracks are different--and it looks to me that the authors are
> >>>>> overstating the case for the similarity -- then we have to balance
> >>>>> this against the fact that our *Tiktaalik* fossils come later in time
> >>>>> than those of the fish that it represents the next step from on the
> >>>>> way to tetrapods. Why should these "relicts" show up in the order in
> >>>>> which they supposedly arose over ten million years earlier?
>
> >>>> Better question: why shouldn't they? We're talking about a handful of
> >>>> fossils, for which any order would be likely enough even if it were
> >>>> random.
of undeserved luck. The researchers were going on the supposition
that something intermediate in time between these earlier lobefins and
tetrapods would have been in rocks dated at a certain date, and lo!
they were right.
> >>>>> And *Tiktaalik* really looks like a fine transitional from
> >>>>> Eusthenopteron types to tetrapods. I refer you not only to the
> >>>>> University of Chicago website above but also to the two seminal
> >>>>> articles on this theme:
> >>>>> (6 April 2006):
> >>>>>http://www.nature.com/nature/journal/v440/n7085/pdf/nature04639.pdf
> >>>>> (16 October 2008):
> >>>>>http://www.nature.com/nature/journal/v455/n7215/full/nature07189.html
>
> >>>> Yes, and dromaeosaurs are fine transitionals too despite being mostly
> >>>> much later than Archaeopteryx. So?
> >>>>> The authors of the main article don't do a very good job of meeting
> >>>>> that objection:
> >>>>> ...why do the elpistostegids appear before
> >>>>> tetrapods in the body fossil record in a manner
> >>>>> that neatly simulates a stratophylogenetic fit (Fig. 5)?
> >>>>> ...
> >>>>> If their first appearance as body fossils reflects
> >>>>> the time when they first colonized environments
> >>>>> with preservation potential, as seems likely, the
> >>>>> elpistostegids evidently arrived in advance of the
> >>>>> tetrapods. The reason was presumably ecological
> >>>>> but cannot be determined at present.
> >>>>>http://www.nature.com/nature/journal/v463/n7277/full/nature08623.html
> > The mainstream theory is that the tetrapods are a monophyletic
> > group. If this is true, then there is a most recent common ancestor
> > (MRCA) from which all the extant tetrapods are descended.
>
> That's true regardless of whether they're monophyletic.
"tetrapod" before "MRCA."
> > However, the
> > mainstream still doesn't know where this MRCA lived.
> > The conventional wisdom (e.g., comic books) is that the MRCA of
> > tetrapods lived mostly on land. According to this view, the MRCA was
> > an amphibian whose life cycle vaguely resembled the life cycle of
> > today's amphibians. This means that juveniles lived in fresh water and
> > the adults lived on land.
identify "The main problem here" the way you do.
> The main problem here is confusion over what is meant by "tetrapod". If
> we're going by extant species, i.e. the ancestor of crown group
> Tetrapoda, then the inference is most probably correct.
even worth talking about in the context of Tiktaalik--or Darwin123's
last paragraph.
> If you mean some
> other group, the answer depends on what other group you mean. There
> really is no way to tell from this post what you're talking about.
is useful for this discussion. [See above.]
We mathematicians are familiar with the concept of "intended meaning"
and proceed as though we had got it right, perhaps inquiring whether
we really did get it right. Do systematists have a different *modus
operandi*?
Remainder deleted, due to shortage of time today.
Peter Nyikos
pnyikos
below due to lack of time." I admit that the word "extant" is
generally understood to mean "living", but I think, in view of the
whole context, that he meant "of which we have specimens"--which
includes species known only from fossils.
John Harshman
>>>>>> Yes, and dromaeosaurs are fine transitionals too despite being mostly
>>>>>> much later than Archaeopteryx. So?
>
> "mostly"? do you know of any exceptions?
are increasing numbers of other Jurassic maniraptorans.
>
>>> The mainstream theory is that the tetrapods are a monophyletic
>>> group. If this is true, then there is a most recent common ancestor
>>> (MRCA) from which all the extant tetrapods are descended.
>> That's true regardless of whether they're monophyletic.
>
> Sure, but Darwin123's statement regains its relevance if you add
> "tetrapod" before "MRCA."
group, right? The group you specifically state is not relevant. So what
group is he talking about? Use your ESP skills to divine that and tell
me, if you will.
>>> However, the
>>> mainstream still doesn't know where this MRCA lived.
>>> The conventional wisdom (e.g., comic books) is that the MRCA of
>>> tetrapods lived mostly on land. According to this view, the MRCA was
>>> an amphibian whose life cycle vaguely resembled the life cycle of
>>> today's amphibians. This means that juveniles lived in fresh water and
>>> the adults lived on land.
>
> The above seems clear enough to me. I can't understand why you
> identify "The main problem here" the way you do.
>> The main problem here is confusion over what is meant by "tetrapod". If
>> we're going by extant species, i.e. the ancestor of crown group
>> Tetrapoda, then the inference is most probably correct.
>
> You mean the MRCA of the crown group. That came so late, it isn't
> even worth talking about in the context of Tiktaalik--or Darwin123's
> last paragraph.
>
>> If you mean some
>> other group, the answer depends on what other group you mean. There
>> really is no way to tell from this post what you're talking about.
>
> Really, there is only one way to interpret Darwin123's statement that
> is useful for this discussion. [See above.]
way is not.
> We mathematicians are familiar with the concept of "intended meaning"
> and proceed as though we had got it right, perhaps inquiring whether
> we really did get it right. Do systematists have a different *modus
> operandi*?
exactly did Darwin123 mean by "tetrapod"? I couldn't tell from his post,
and I can't tell from your post. If "tetrapod" is meant to include
Ichthyostega, for example, then the MRCA of tetrapods most probably did
not live on land.