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Re: Endothermic Crocs in Nature



Tim Williams wrote-

> To be fair, and as you allude to, the original material for
_Macelognathus_
> was very scrappy.  As Gohlich et al. (2005) say: "_Macelognathus vagans_
was
> described by O.C. Marsh in 1884, based on a mandibular symphysis... New
> material of this species from the Morrison Formation of western Colorado
> demonstrates its affinities with basal crocodylomorphs ..."  Marsh and his
> successors could be forgiven for not knowing the precise identity of
> _Macelognathus_.

Even though the holotype is fragmentary, even the new specimens are
surprisingly dinosaur-like.  It may just be that I'm unfamiliar with
sphenosuchians, but things like the large dorsal neural canals, anterior
dorsal hypapophyses, apparent cuppedicus fossa, fairly long pre- and
postacetabular processes, inturned femoral head, inturned cnemial crest and
generally elongate hindlimb elements seem quite dinosaurian to me.  I don't
blame Ford for thinking the mandibles could be from an oviraptorosaur,
especially considering what we now know about the dentition of basal forms.
Of course, the calcaneum is clearly crurotarsan, but still, the convergence
is striking.

> Greg cites this in support of "neoflightlessness" in early birds.  This
> "rule" makes a great deal of intuitive sense; but I have yet to see any
hard
> evidence (e.g., similar reversions of incipient or nascent ecomorphologies
> in other lineages).  For example, I know of no "neoflightless" insects,
nor
> "neoamphibious" proto-cetaceans.

No neoflightless insects?  Every flightless pterygote is neoflightless.
Including some in basal clades like Dermaptera, Grylloblattidae and
Dictyoptera.  Of course, plenty of derived insects are neoflightless as well
(fleas, lice, etc.).

Mickey Mortimer
Undergraduate, Earth and Space Sciences
University of Washington
The Theropod Database - http://students.washington.edu/eoraptor/Home.html