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Thecodont pelage (and scutes)



Mike,
The scutes of carnotaurines would presumably be the transformed remnants of the original "thecodont pelage", and the groups you mentioned are big gigantothermic-like animals (most would have been relatively pelage-free, like elephants, but who knows, there may have been hairy mammoth-like analogs in colder areas that will eventually be found, in some larger Jurassic or Cretaceous dinosaurs).
And Longisquama "scutes" could be an intermediate form that began developing a feather-like structure independently of the line leading to dinobirds. Whether you want to call it parallelism or convergence would be somewhat arbitrary if they developed from homologous structures (and protofeathers and scutes appear to be homologous). I just wish we had a Longisquama tail, as I bet there were shorter such structures covering the tail (and perhaps extending beyond the end of the tail if they had a predator evasion purpose).
Of course, if the development of "thecodont pelage" began in the Permian, my proposed "predator evasion" (tail pelage) strategy may have been just a Permian phenomenon, exapted for brooding and even internal thermoregulation by Early Triassic times. The more I think about it, the more I like this "tail-first" hypothesis.
--------Ken Kinman
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From: "T. Mike Keesey" <tmk@dinosauricon.com>
Reply-To: tmk@dinosauricon.com
To: -Dinosaur Mailing List- <dinosaur@usc.edu>
Subject: Re: Archosaur Origins...was:MESENOSAURUS ERRATA.
Date: Sat, 25 Aug 2001 19:06:28 -0400 (EDT)

On Sat, 25 Aug 2001 Dinogeorge@aol.com wrote:

> With regard to integument, I was referring to that of possible >arboreal
> prolacertiforms<. If pterosaurs are prolacertiform descendants, then it is
> quite possible that some prolacertiforms already had the kind of hairlike
> "pelage" that is well known in pterosaurs.


IIRC, there are possible hairlike structures in _Cosesaurus_.

> This may, in turn, have also appeared other prolaceriforms, such as
> those from which those animals widely known as archosaurs evolved,

Are you using Prolacertiformes as a doubly paraphyletic group of
non-pterosaurian, non-archosauriform archosauromorphs?

Has it ever been defined as a clade? Clade(_Prolacerta_ <-- _Passer_,
_Crocodylus_) might work well, although then it could be synonymous with
_Pterosauromorpha_.

> and it may have been preserved in the arboreal
> lineages that led to birds and dinosaurs. Secondary loss of hairlike
> "pelage," or conversion to smooth scutes, might be expected in aquatic
> reptiles such as proterosuchians, so absence of hairlike "pelage" in these
> groups does not preclude its existence in ancestral prolacertiforms.


Interesting, although that doesn't explain the lack of hairlike pelage in
terrestrial forms such as ceratopsids, hadrosaurids, titanosaurs, and
carnotaurines.

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T. MICHAEL KEESEY
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