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Re: Psittacosaurid Revelations

Gunter van Acker (guntervanacker.mesozoic@pi.be) wrote:

<With both maniraptorans (neornitheans, deinonychosaurs,
compsognathids, therizinosaurs ...) and psittacosaurs having
keratinous integumentary structures, this could mean that these
structures are basal for Dinosauria and even Ornithodira.>


<If keratinous integument was basal for Ornithodira, then the
following could be applicable;

1. the primitive condition of this integument became hair-like and
formed a kind of  "fur" in pterosaurs (cf. Sordes)>


<Conclusion : the possession of keratinous integument was truly basal
for Ornithodira and had initially evolved only for heat-regulating
purposes. Some smaller theropods were able to evolve the integument
into complex feathers that were eventually used for powered flight,
most other dinosaurs increased in size and soon lost the integument
or only retained remnants. If this basal nature of the integument
proves to be correct, this would mean that all dinosaurs were
endothermic. The fully erect position of the dinosaur hindlimbs was
(as far as I am concerned) the first indication of a possible
endothermy of Dinosauria.>

  It seems a critically important fact has been left out, not to
imply that Gunter's abilities in this analysis are lacking; they are
not. Some evolutionary measures have been lost to the wayside in the
strictest or classic assumption of the meaning of Ornithodira.

  By most recent analysis, it seems likely that the Pterosauria is
nested withing the Prolacertiformes, leaving several of these animals
having a good stretch of evolution between them and dinosaurs, like
the Archosauria and all the crocodiles and non-furry animals that are
brought up by the term "croc-like." Thus, Ornithodira may be
synonymous with the Archosauromorpha. On the other hand, the form of
dorsal scutes in dinosauromorphs like *Lewisuchus* (which is closer
to dinosaurs than even *Lagosuchus* is) suggests that any
intermediate in an Archosaur-only Ornithodira [where pterosaurs are
the sister group to dinosaurs without croc intermediaries] would not
have had much extensive extra-integumental coverage, despite
pterosaurs having fully clothed trunks.

Jaime A. Headden

  Where the Wind Comes Sweeping Down the Pampas!!!!

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