Re: integument (Re: Dinosaur Were Endotherms (sic))

[Jonkeria <Jonkeria@aol.com>]

In a message dated 98-04-04 03:01:37 EST, Tracy wrote:

<< Last year I was walking around the SVP and I over heard someone say they
had skin impressions 
 from a Dimetrodon. I don't know any more that that. At least its one early
animal.>>

I thought I heard something to this effect as well. Anyway, fossilized
integument is known for a dinocephalian therapsid, Estemmenosuchus, and it is
definitely NOT scaly, but is rather soft and glandular and rather like a
purely terrestrial version of "amphibian" skin, strongly suggesting that this
type of skin is the primitive state for the terrestrial vertebrates and scales
evolved later and separately in various animals. (I'm pretty sure Dimetrodon
had the soft glandular skin too, if I remember what I heard.)

<<There are skin impressions of early animotes, ie. Labyrinthodon's, and they
have scales.
 So artist need to take this into account when they do drawings. For example,
Metoposaurids have 
 scales, and didn't have skin like modern amphibians. They did not look like a
Helibender (sic).>>

I did not know skin was known for *Labyrinthodon* (I also did not know it was
an "animote", [I know, you mean amniote]--thought it formed the basis for the
rather basal and rather large tetrapod group the labyrinthodont temnospondyls.
[Didn't that genus also get synonomized with something else at some time?])
But these temnospondyl scales (known also in Trimerorhacis, I believe)
probably evolved independently of the main path (that is, reptilian) of scale
evolution and there is no reason to think all early tetrapods (including
amniotes) had them. Scale convergence factor (that is, the propensity for
several groups to evolve scale structures independently of the main, soft-
skinned line) is well-illustrated by the albanerpetonids, a small group of
Jurassic to Miocene amphibians that were covered in little polygonal scales.
Yet, these animals are very close to the other true amphibians (some analyses
have placed them between the Caudata and the "microsaurs") which of course
have the soft, scaleless skin.
 
-Christian Kammerer