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Re: Platyhystrix and dinosaur humps/sails

While I think is probable that sails would have been use for display (nature wouldn't waste so much advertising space) the fact that this feature is found mainly in unrelated animals living in the same environment makes me think it served primarily some other purpose. I'll list the things I've noted, and people can correct me if they like:

Tall spines occur in a few different groups: amphibians, "pelycosaurs", dinosaurs, and mammals come into play here. Of them, dimetrodon and friends have thin spines that probably supported a sail, Platyhystrix had flat broad ones that supported part of one, mammals have flat ones that make a hump, and spinosaurs and ouranosaurs have flat spines that could have been either.

I dunno... sails on such large dinosaurs would have been quite delicate, but it seems to me a large hump would make them awfully slow and prone to enemies.


From: crnoto@midway.uchicago.edu (Chris Noto)
To: m38jeep@hotmail.com
Subject: Re: Platyhystrix and dinosaur humps/sails
Date: Tue, 7 Mar 2000 08:42:37 -0600

I'm just curious, what good would a large, ungainly hump (especially one 6
ft tall in the case of Spinosaurus) be to a predator?  Furthermore, didn't
Suchomimus inhabit broad river deltas? It too  had a low sail, but didn't
neccesarily inhabit hot environments.  I'm all  for the sexual display
theory myself, at least as it relates to the dinosaurs.

Chris

>>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
>>
>>
>So, if Platyhystrix is known to have a sail, has anyone ever compared its
>spines to one of the high-spined dinosaurs? I'm not really partial to either
>the hump or the sail theory at present, but wouldn't an amphibian with
>broad, flat spines that form a sail go against the hump theory in
>Spinosaurus and Ouranosaurus?
>
> -M. Nalasco
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-----------------------------------
Chris Noto
University of Chicago
c-noto@uchicago.edu
(773) 947-0734

"If I had a good quote I would put it here."



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