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Ancient walking mystery deepens
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Metspitzer
May 23, 2012, 10:16:25 PM5/23/12
to
One of the first creatures to step on land could not have walked on
four legs, 3D computer models show.
Textbook pictures of the 360-million-year-old animal moving like a
salamander are incorrect, say scientists.
Instead, it would have hauled itself from the water using its front
limbs as crutches, research in Nature suggests.
The move from living in water to life on land - a pivotal moment in
evolution - must have been a gradual one.
Ichthyostega is something of an icon in the fossil world. Living
during the Upper Devonian period, it was dubbed a "fishapod", with its
mixture of fish-like and amphibious features.
Although it probably spent much of its time under water, at times it
was thought to have crawled halfway up onto land on limb-like
flippers.
Exactly how it moved on land has been a matter of much debate,
however.
Now, a team from The Royal Veterinary College, London and the
University of Cambridge, has spent three years reconstructing the
first 3D computer model of Ichthyostega from fossils.
It enabled them to study how ancient vertebrates made the "monumental
transition" from swimming to walking.
Study author Dr Stephanie Pierce, of The Royal Veterinary College,
said the 3D skeleton allowed them to calculate the range of movement
in the joints of its limbs for the first time.
http://richarddawkins.net/articles/646001-ancient-walking-mystery-deepens
four legs, 3D computer models show.
Textbook pictures of the 360-million-year-old animal moving like a
salamander are incorrect, say scientists.
Instead, it would have hauled itself from the water using its front
limbs as crutches, research in Nature suggests.
The move from living in water to life on land - a pivotal moment in
evolution - must have been a gradual one.
Ichthyostega is something of an icon in the fossil world. Living
during the Upper Devonian period, it was dubbed a "fishapod", with its
mixture of fish-like and amphibious features.
Although it probably spent much of its time under water, at times it
was thought to have crawled halfway up onto land on limb-like
flippers.
Exactly how it moved on land has been a matter of much debate,
however.
Now, a team from The Royal Veterinary College, London and the
University of Cambridge, has spent three years reconstructing the
first 3D computer model of Ichthyostega from fossils.
It enabled them to study how ancient vertebrates made the "monumental
transition" from swimming to walking.
Study author Dr Stephanie Pierce, of The Royal Veterinary College,
said the 3D skeleton allowed them to calculate the range of movement
in the joints of its limbs for the first time.
http://richarddawkins.net/articles/646001-ancient-walking-mystery-deepens
Richard Norman
May 23, 2012, 10:52:48 PM5/23/12
to
On Wed, 23 May 2012 22:16:25 -0400, Metspitzer <Kilo...@charter.net>
wrote:
Three-dimensional limb joint mobility in the early
tetrapod Ichthyostega
Stephanie E. Pierce, Jennifer A. Clack & John R. Hutchinson
doi:10.1038/nature11124
http://www.nature.com/nature/journal/vaop/ncurrent/full/nature11124.html
"We show that Ichthyostega could not have employed typical tetrapod
locomotory behaviours, such as lateral sequence walking. In
particular, it lacked the necessary rotary motions in its limbs to
push the body off the ground and move the limbs in an alternating
sequence. Given that long-axis rotation was present in the fins of
tetrapodomorph fishes, it seems that either early tetrapods evolved
through an initial stage of restricted shoulder and hip joint mobility
or that Ichthyostega was unique in this respect. We conclude that
early tetrapods with the skeletal morphology and limb mobility of
Ichthyostega were unlikely to have made some of the recently described
Middle Devonian trackways."
wrote:
tetrapod Ichthyostega
Stephanie E. Pierce, Jennifer A. Clack & John R. Hutchinson
doi:10.1038/nature11124
http://www.nature.com/nature/journal/vaop/ncurrent/full/nature11124.html
"We show that Ichthyostega could not have employed typical tetrapod
locomotory behaviours, such as lateral sequence walking. In
particular, it lacked the necessary rotary motions in its limbs to
push the body off the ground and move the limbs in an alternating
sequence. Given that long-axis rotation was present in the fins of
tetrapodomorph fishes, it seems that either early tetrapods evolved
through an initial stage of restricted shoulder and hip joint mobility
or that Ichthyostega was unique in this respect. We conclude that
early tetrapods with the skeletal morphology and limb mobility of
Ichthyostega were unlikely to have made some of the recently described
Middle Devonian trackways."
DougC
May 24, 2012, 10:33:29 PM5/24/12
to
Metspitzer wrote:
> The move from living in water to life on land - a pivotal moment in
> evolution - must have been a gradual one.
Consider the evolution of insects, of all sort and size. Did they
> The move from living in water to life on land - a pivotal moment in
> evolution - must have been a gradual one.
first appear in the water?
Kleuskes & Moos
May 25, 2012, 12:41:39 PM5/25/12
to
Richard Norman
May 25, 2012, 1:51:37 PM5/25/12
to
million years ago. The millipedes and centipedes had already been on
land some 20 million years. This is a change from earlier ideas that
insects evolved from the millipede-centipede group. Unfortunately
there are no good fossil records connecting the freshwater brachiopod
crustacea to the earliest insects. It is believed, though, that the
insects originated in fresh water and then invaded land rather than
having brachiopods invading land and then turning into insects.
Glenner at al. in "The Evolution of Insects" says: "The successful
colonization of the terrestrial environment by hexapods seems to
coincide with other major groups of land pioneering animals such as
the chelicerates and the myriapods in the Late Silurian and the
tetrapods (amphibians, reptiles, birds, and mammals) in the Late
Devonian. All these events appear to have occurred through a
freshwater dwelling phase in their evolutionary transition from marine
to true terrestrial animals. The Devonian is believed to have
been a time of severe drought, which might have forced these animals
(at least hexapods and tetrapods) onto land as their freshwater
habitats vanished."
Science 314:1883-1884(22 Dec 2006).
Kleuskes & Moos
May 27, 2012, 5:50:47 AM5/27/12
to
to coincide, like rising oxygen levels and/or overpopulation of aquatic
environments?
Richard Norman
May 27, 2012, 7:28:16 AM5/27/12
to
On Sun, 27 May 2012 09:50:47 +0000 (UTC), Kleuskes & Moos
The article ends with mention of drought in the Devonian. Also it was
the earlier invasion of land by plants. There was an incredible
abundance of oxygen, something often lacking in stagnant water, and
originally absolutely no predators so that when the land plants
started growing the presence of food made for a very nice habitat. Of
course there were three really powerful problems that needed to be
solved: how to support yourself from gravity when there is no
buoyancy, how to protect yourself from dessication, and how to get the
sperm to the egg if it can't just swim in the surrounding water. The
arthropod exoskeleton and vertebrate bony skeleton, already useful in
water, easily answered the first two problems. The third required
internal fertilization which the aquatic arthropods I believe had
already developed at least partially. Tetrapods solved the third by
returning to water to reproduce until the penis-vagina business could
develop along with the amniotic egg that could survive on land.
the earlier invasion of land by plants. There was an incredible
abundance of oxygen, something often lacking in stagnant water, and
originally absolutely no predators so that when the land plants
started growing the presence of food made for a very nice habitat. Of
course there were three really powerful problems that needed to be
solved: how to support yourself from gravity when there is no
buoyancy, how to protect yourself from dessication, and how to get the
sperm to the egg if it can't just swim in the surrounding water. The
arthropod exoskeleton and vertebrate bony skeleton, already useful in
water, easily answered the first two problems. The third required
internal fertilization which the aquatic arthropods I believe had
already developed at least partially. Tetrapods solved the third by
returning to water to reproduce until the penis-vagina business could
develop along with the amniotic egg that could survive on land.
Steven L.
May 27, 2012, 7:43:29 AM5/27/12
to
"Richard Norman" <r_s_n...@comcast.net> wrote in message
news:ma34s7po5e3ns8itl...@4ax.com:
true land-dwellers.
-- Steven L.
Richard Norman
May 27, 2012, 9:44:10 AM5/27/12
to
jillery
May 27, 2012, 1:38:09 PM5/27/12
to
sorted out.
pnyikos
May 28, 2012, 8:01:30 AM5/28/12
to nyi...@math.sc.edu
On May 25, 1:51 pm, Richard Norman <r_s_nor...@comcast.net> wrote:
> On Fri, 25 May 2012 16:41:39 +0000 (UTC), Kleuskes & Moos
>
> On Fri, 25 May 2012 16:41:39 +0000 (UTC), Kleuskes & Moos
>
> <kleu...@somewhere.else.net> wrote:
> >On Thu, 24 May 2012 19:33:29 -0700, DougC wrote:
>
> >> Metspitzer wrote:
>
> >>> The move from living in water to life on land - a pivotal moment in
> >>> evolution - must have been a gradual one.
>
> >> Consider the evolution of insects, of all sort and size. Did they
> >> first appear in the water?
>
> >Good question.
>
> Insects seem to have evolved from freshwater crustacea around 410
> million years ago. The millipedes and centipedes had already been on
> land some 20 million years. This is a change from earlier ideas that
> insects evolved from the millipede-centipede group. Unfortunately
> there are no good fossil records connecting the freshwater brachiopod
> crustacea to the earliest insects.
Correct spelling: branchiopod
> >On Thu, 24 May 2012 19:33:29 -0700, DougC wrote:
>
> >> Metspitzer wrote:
>
> >>> The move from living in water to life on land - a pivotal moment in
> >>> evolution - must have been a gradual one.
>
> >> Consider the evolution of insects, of all sort and size. Did they
> >> first appear in the water?
>
> >Good question.
>
> Insects seem to have evolved from freshwater crustacea around 410
> million years ago. The millipedes and centipedes had already been on
> land some 20 million years. This is a change from earlier ideas that
> insects evolved from the millipede-centipede group. Unfortunately
> there are no good fossil records connecting the freshwater brachiopod
> crustacea to the earliest insects.
Brachiopods are, of course, a separate phylum, sporting a "living
fossil" *Lingula*. This was once believed to go back 500 million
years, but the Wikipedia entry is more cautious, saying only that
"similar genera" go back to Ordovician times.
http://en.wikipedia.org/wiki/Brachiopod
> It is believed, though, that the
> insects originated in fresh water and then invaded land rather than
> having brachiopods invading land and then turning into insects.
Peter Nyikos
Professor, Dept. of Mathematics -- standard disclaimer--
University of South Carolina
http://www.math.sc.edu/~nyikos/
nyikos @ math.sc.edu
Richard Norman
May 28, 2012, 8:29:44 AM5/28/12
to
Thank you for the correction. I do know the difference and should
have been more careful.
There are a very few species of insects that are truly marine, five
species of Halobates, although many live in coastal marine
environments.
See
http://mbrd.ucsd.edu/Research/labs/Cheng/Halobates%20Revewlower.pdf
.
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