RE: bipedal crocodylomorphs

[Tim Williams <twilliams_alpha@hotmail.com>]

John R. Hutchinson wrote:

> I haven't seen Huene's original _Saltoposuchus_ (iirc) paper and am 
> wondering if it stems from there, or something else I've missed in the 
> disparate crocodylomorph literature.

I've not actually read or seen Huene's description of _Saltoposuchus_, but I 
know Huene (1936) included a figure of a skeletal reconstruction of a 
bipedal _Saltoposuchus_.  Colbert (1952) and Romer (1972) also figured 
_Hesperosuchus_ and _Gracilisuchus_ as bipeds.  Back then, these critters 
were assumed to be 'pseudosuchian thecodonts' rather than basal 
crocodylomorphs.  Pseudoschians were assumed to be the stock from which 
dinosaurs (or at least to theropods) and birds evolved, so it made sense to 
restore the sphenosuchians as bipeds (like _Ornithosuchus_, another 
'pseudosuchian thecodont').  I think the idea of bipedal sphenosuchians was 
more typological than anything else.

Unlike its Triassic brothers, _Hallopus_ was originally regarded as a 
coelurosau.  But is any forelimb material known for _Hallopus_?

> I've found very few explicit and detailed discussions of the evidence in 
> the
> literature, compared with much discussion of quadupedal features.

The best I can come up with is Benton and Walker (2002), who mention bipedal 
sphenosuchians in the context of possible facultative bipedalism in the 
basal archosaur _Erpetosuchus_:

"The relatively slender pectoral girdle and forelimb suggest that 
_Erpetosuchus_ may have been a facultative biped.  Clearly, without the 
hindlimbs, it is impossible to be sure, but _Erpetosuchus_ shows similar 
proportions of the skull, neck and forelimbs to the facultatively bipedal 
sphenosuchian crocodylomorph _Terrestrisuchus_ (Crush, 1984), as well as to 
_Scleromochlus_, the dinosauromorphs _Lagerpeton_ and _Marasuchus_, and 
basal dinosaurs (Sereno & Arcucci, 1994a,b; Benton, 1999).  If 
_Erpetosuchus_ were a cursor, it may not have used its forelimbs in running, 
since the radius is shorter than the humerus (in cursors, the distal limb 
element is often longer than the proximal (Hildebrand, 1974)).

I haven't read Crush (1984), but it may have something on facultative 
bipedalism in sphenosuchians.

References

Crush, P.J. (1984). A late Upper Triassic sphenosuchid crocodilian from 
Wales. Palaeontology 27: 131-157.

Benton, M.J. and Walker, A.D. (2002).  _Erpetosuchus_, a crocodile-like 
basal archosaur from the Late Triassic of Elgin, Scotland.  Zoological 
Journal of the Linnean Society 136: 25 -47.




Tim