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Thecodont pelage (and scutes)
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.
From: "T. Mike Keesey" <email@example.com>
To: -Dinosaur Mailing List- <firstname.lastname@example.org>
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
> quite possible that some prolacertiforms already had the kind of
> "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
> 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
> 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
T. MICHAEL KEESEY
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