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RE: bipedal crocodylomorphs



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