From: AM Yates <Adam.Yates@bristol.ac.uk>
Reply-To: Adam.Yates@bristol.ac.uk
To: Mary Nalasco <m38jeep@hotmail.com>
CC: DINOSAUR@USC.EDU
Subject: Re: Platyhystrix and dinosaur humps/sails
Date: Tue, 7 Mar 2000 09:46:01 +0000 (GMT)
On Tue, 7 Mar 2000, Mary Nalasco wrote:
> Hello, all-
>
> I was going through some of my books and came across a picture of the
> sailbacked amphibian, Platyhystrix. The spines on its back resembled
those
> of Spinosaurus and Ouranosaurus- flat and blade-like. I've never seen
its
> skeleton, just a few illustrations, but I was wondering this: if we were
to
> say dinosaurs have humps because their spines resemble humped mammals,
> shouldn't we say the same for Platyhystrix?
I have seen the vertebrae of Platyhistrix (to my knowledge there is no
complete skeleton) and although the neural spines were flat and blade
like a hump is out of the question. The sides of spines are ornamented
with rough pits and bumps which in amphibian fossils indicates a close
association with a thin skin or possibly even a horny covering. There is
a sharp line between the rough
ornamented bone and the smooth bone over which muscles and other tissues
lay. The genus Aspidosaurus may be paraphyletic with respect to
Platyhistix (ie. contains its ancestor) and shows that the spines
evolved from a vertebral series of armour plates that fused to the
nueral spines and grew tall. The show every intergrade from low bumps to
tall Platyhistrix like spines. Further more well preserved spines show
that web of skin between the spines did not extend all the way to the
top of the sail (it only goes halfway up or less). This was probably the
case in Platyhistrix as well but poorer preservation of the material
I've seen made this hard to determine.
cheers
Adam Yates