Re: H2O Preds. and AAT

chris brochu (
28 Sep 1995 00:41:44 GMT

I agree with many of your points. However, I'd like you to clarify what
you mean by "distribution of crocodiles in the past."

If you mean, "meter by meter frequency distribution of large adult
Crocodylus lloydi (the large Pliocene form)," you're right. We don't
know that, and we never will.

On the other hand, if you mean, "which bodies of water had crocs and
which didn't," we actually have some relevant data. Eitan Tchernov wrote
a monograph on Tertiary and Pleistocene crocodylids of western and
northern Africa (1986, CNRS), and a revision, largely based on the Lake
Turkana crocs, is in the works by Glenn Storrs. Crocodylians have a
fantastic fossil record - they lived in great environments for
preservation, and their bone is rather dense. As far as we can tell, if
it was wet, there were crocs.

As for crocs decimating a population; I'm going out on a limb here, but
yes, I do think crocs could have nearly eradicated a population of
semiaquatic forms similar to us. Unlike lions, who select an individual
from a herd, crocs will congregate in numbers and snap away at anything
that moves. Fish aren't hurt much by this because (a) they swim well and
can get away, and (b) occur in very large numbers. Hippos escape this by
being large. In fact, there are records of hippos killing crocs. If the
population dynamics of non-human primates are informative, early hominids
probably occurred in not-so-large social groups. IMHO, they would be
forced out of the water as soon as one or a few were taken, and sooner or
later would learn to not go back in.

A good model might be the gnu herds that migrate every year. The crocs
take hundreds. The only reason the gnu aren't eradicated is that they
spend as little time as possible in the water - they cross and get out.
As soon as the crocs sense a clumsy intruder, they're on their way.

Again, my caveat - my research is on crocs, not primates. If my
understanding of hominid population struture is off, I apologize.