Re: Platyhystrix and dinosaur humps/sails

["Stephen Priestley" <sn2192@uniserve.com>]

Larry Febo wrote:
> As far as Dimetrodon goes, I`ve always thought of it`s sail as a
> "heat-dumping" mechanism. Especially if it was on an evolutionary path
> towards increasing endothermy. They were rather large animals, and
probably
> lacked the sweat glands that were to appear in later mammals. ( I wonder
if
> therapsids had sweat glands??). Perhaps they were also used for heat
dumping
> in the aforementioned dinos. ...especially if these dinos were inhabiting
> excessively hot enviornments, and their "avian style" respiratory systems
>  assuming they had such) were alone not sufficient to cool these large
> animals down.
> 
Using sails for heat regulation makes alot of sense. I'm guessing that the
relative size of the sail would be determined, in part, by the animals'
balance. Sail-backed pelycosaurs and_Platyhystrix_  all had tall neural
spines and a sprawling stance, bipedal _Spinosaurus_  had shorter neural
spines. To ease discomfort in a strong wind, pelycosaurs likely just
aligned themselves nose-on to the breeze. What effect would an equally
strong gust have on a hypothetical spinosaur with a pelycosaur-sized fin? I
envision one startled, top-heavy dinosaur lying on its side again.

(From Adam Yates' description of _Aspidosaurus_, it sounds like
_Platyhystrix_ may have had a dual purpose fin. Or, if the top half of the
neural spine was horn-covered, maybe its fin was primarily for protection
and display.)