BIRDY CROCS?

["Matthew Troutman" <m_troutman@hotmail.com>]

<<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.  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).  Wonder why it wasn't 
interpreted that way in theropod=>bird circles (some are working on 
this).  He goes on to list several other arboreal specializations in 
_Sphenosuchus_ (which are also present in maniraptoriforms).  

<<'(14) Crocodilians were originally arboreal as evidenced by the 
climbing ability of juvenile crocodilians, the morphology of the 
tarsus, long humerus, pneumatization of the skull and limbs of 
fossils crocodilomorphs, marked inward and forward curvature of the 
lower half of the tibia and reduction of the first metatarsal.'>>

Don't forget Martin's _Current Ornithology_ paper in 1983.  He lists 
this feature as equivocal for some reason.  

I think that arboreality as being primitive among crocodylomorphs to be 
quite an interesting notion, though I will hold out making radical 
speculations until more evidence is found.  

Now to the birdy croc section of this post.....

There are actually two versions of the crocodile => bird scenario.  1)  
The Walker hypothesis where birds are the sister-group to 
crocodylomorphs and (in later papers) _Sphenosuchus_ is closer to birds 
than crocs.  2)  The Whetstone hypothesis where birds share a special 
common ancestor with Crocodylia (Crocodyliformes actually) and 
sphenosuchids are the sister to the bird+croc clade.  If there was no 
evidence for the maniraptoriform => bird theory, I would go with the 
croc hypothesis and the Whetstone version, but, as noted in a recent 
post by Darren, the braincase evidence, which the croc hypothesis hinges 
on, is more in line with the theropod hypothesis (kick ass!).  

Anyway, while birdy crocs are interesting, I doubt that anybody 
(including me) can part with the birdy theropod image.  

Matt Troutman 
m_troutman@hotmail.com


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