On Saturday, November 22, 2014 11:55:14 PM UTC-5, Oxyaena wrote:
(Paul Ciszek) wrote:
> > So, there have been claims for some time now that ctenophora are a
> > sister-group to all other metazoans, and recent genetic studies
> > have re-inforced this.
Molecular classifications seem to have completely pushed morphological
ones aside -- wherever there is a discrepancy between them, the "consensus"
seems to be that the molecular systematics is the one to follow.
Morphologically, it seems to make no sense for poriferans to be descended
from ctenophores--at least, not ctenophores like the ones we see.
> > Clade-wise, some node splits into ctenophra
> > and porifera, and eumetazoa branch out of one of the types of
> > porifera. Or probably one node branched out into the porifera we
> > know about and some other porifera that we don't, and the ctenophora
> > branched out of a type of porifera that isn't around anymore.
> > Elsewhere, Wiki claims that extant ctenophores probably descend from
> > a common ancestor as recently as the KT extinction event.
If so, that ctenophore was a "living fossil" since ctenophore fossils
almost indistinguishable from living ones, morphologically, have been
found in the Chengyang shales from 520 or more million years ago. There
is an exquisite photograph of one of these fossils in _Darwin's Doubt_,
by Stephen Meyer.
> > Putting this two together, I read that to mean that there used to be
> > an entire sub-kingdom of metazoa, more different from us than we are
> > from sponges, that was reduced to a single species by the KT event.
> > Am I interpreting this stuff correctly?
I believe you are not. Calling something a subkingdom simply because
it branched off from other extant representatives of a kingdom,
and assuming that this "ghost subkingdom" was full of alien-seeming
creatures, makes for poor systematics. Ever since the cladophiles have
banished taxa higher than species and genus, and all paraphyletic taxa,
this kind of talk is creeping in.
> > What other subkingdoms might we have lost completely in, say, the
> > Permian extinction and aren't even aware that they ever existed?
> Numerous subkingdoms could have been lost, the chance of an organism
> fossilizing is next to nothing, you have to be in the right area for
> fossilization, such as a floodplain, and there are other factors to,
> such as if any scavengers get to the remains, does the dead organism
> have hard parts or is just a blob of soft tissues, etc.
That ctenophore fossil of the Cambrian had an imprint of soft tissues.
Imprints of soft tissues have been preserved in the Burgess shales,
in the Chengyang shales, and quite a few other (but rare and to be treasured)
sites known collectively as Konservat Lagerstaette. You can read about
Wikipedia has a listing of the known ones.
Professor, Dept. of Mathematics -- standard disclaimer--
University of South Carolina
nyikos @ math.sc.edu