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Re: BIRDY CROCS?



><<Moving toward rather less dodgy ground, there have been occasional
>references in the technical literature to occasional arboreality in
>crocs. In one of his papers (either 1972, 1974 or 1977: haven't had time
>to check) Alick Walker cited arboreality in primitive
>crocodylomorphs as a character shared with birds, and noted
>that extant crocodile juveniles apparently preserve this primitive
>behaviour. Reviewing Walker's phylogenetic proposals, Tarsitano and
>Hecht (1980) listed Walker's crocodile-bird characters, and, as
>character (14), wrote..>>
>
>His 1972 paper outlines this.  Actually an extremely interesting paper
>(and before Ostrom 1973; wonder why it didn't catch on :-)), he lists a
>1961 Cott paper (Cott, H. B., Trans. Zool. Soc., 29, 211 (1961)), as a
>reference to arboreality in baby crocs.

I'll have to recheck my copy of Cott,  but I don't recall him saying
anything about croc arboreality.  In any case, much of what Cott wrote was
anecdotal.



Also very interesting, crocs
>have a motion in their wrists very similiar to the wing-folding
>mechanism in bird wrists (functional linkage of wrist and forelimb
>joints of Molnar, 1985).  Walker sites this an arboreal specialization
>(actually a primitive, hold-over specialization).


On this, I disagree with Walker.  The croc wrist is comprised of two very
long proximal elements followed by small, stubby distal elements.  The
motion is very unlike that of a bird, with a great deal of up-and-down
motion rather than the side-to-side movement emphasized in maniraptorans.
The morphology in basal crocodyliforms (e.g. Sphenosuchus) more closely
approximates that of something trying to add an extra segment for
cursoriality.

Derived theropods have a very large distal element (the semilunate), and
the emphasized movement is opposite that of crocs.



chris

Christopher Brochu
Department of Geology
Field Museum of Natural History
Roosevelt Road at Lake Shore Drive
Chicago, IL 60605

312-922-9410 x469