Crocs vs. Parasuchians (was RE: Progress schmogress (was Re: competition))

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

> From: Jean-michel BENOIT [mailto:Jean-Michel.BENOIT@gemplus.com]
>
>
> On the same subject, I've always wondered why Parasuchians disappeared to
> be replaced by real crocs in the same habitats, apparently sharing the
> same global body construction. Was it competition, progress,
> specializations or something else? Or am I mistaken in my assumptions?

Be careful of assuming too much.  While parasuchians (in the Late Triassic)
and crocodylomorphs (of the Jurassic and later) had similar anatomies (and
presumably habits), crocs (broadly defined) of the Late Triassic were NOT
croc (in the narrow sense)-like.

Brochu (and others) can correct me if I'm wrong, but the protosuchids (among
the oldest and most primitive members of Crocodylomorpha with an anatomy
consistent with an at least semi-aquatic habit) are from the Early Jurassic,
and thus do not appear until after the parasuchians were extinct.  Triassic
and Early Jurassic crocodylomorphs are primarily small gracile cursorial
terrestrial forms (the sphenosuchians and the Bernard Price crocodylomorph
referred to "_Pedictosaurus_": see Clark et al. 2000 JVP 20:683-704 for a
recent review).  If anything, early members of the lineage leading to crocs
might have been in more competition with dinosauromorphs than with
parasuchians!

Since the parasuchians were extinct by the end of the Late Triassic (by
whatever reason), before we have evidence of crocodylmorphs with a croc-like
habit, competative exlcusion between these clades seems very unlikely.
Instead, crocodylomorphs seem to have radiated into the niche vacated by the
by-then-missing parasuchians (among other aspects of the croc radiations).

Hope this helps.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
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