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Re: AMNIOTE SCALES
On Mon, 28 Oct 1996, Darren Naish wrote:
> The small, bare-skinned one (aka LN Jeff) writes:
> > SCALES are AMNIOTE traits? I thought Tim Holtz just said synapsid
> > were probably unscaled. What is the formal diagnosis for "Reptilia"?
> > Who diagnosed it originally and when (meaning, why is "amniota" usd
> > by cladists for the common ancestor of turtles, lepidosaurs,
> > archosaurs, AND synapsids instead of "reptilia"?)
> I recently had to chase up a couple of things relating to the life appearance
> of various Carboniferous amphibians, and I've now seen 'scaly' skin in an
> _Eryops_. It was described in _American Journal of Science_ back in the 1920s
> I think. Furthermore, in a paper in _Biological Review_ a couple of decades
> back, Bob Carroll figured ventral scales from various late Palaeozoic
> amphibians, as well as from the basal synapsid _Ophiacodon_.
> (Sorry I haven't posted full refs: will do if anyone badgers me.)
> I don't mean to say that Tom is *wrong*, but, hell, I'm confused. Or am I just
> out of date? Jeff, don't call him Tim: just makes him mad.
Scales are definately primitive for the Tetrapoda. They were present in
the imediate tetrapod outgroups (panderichthyids and other more distant
osteolepiforms), in the most basal stem tetrapods (they can be seen in
Jarvik's paper on the tail of Ichthyostega) and were present in the
Anthracosaurs (?stem amniotes, though not if Laurin is to be believed).
They are most certainly present in the Temnospondyli (which most regard
as stem lissamphibians). They are also present in the undoubted
near-amniote Westlothiana. All this means that scales were probably
present in the tetrapod common ancestor and the amniote common ancestor
and were independantly lost somewhere along the lines to lissamphibians
and to mammals. I think it is the fused scales and non-glandular skin
that are apomorphic for Reptilia.
"Oh boy, I got to mention Temnospondyli!"