Re: AAT Theory
chris brochu (gator@mail.utexas.edu)
25 Sep 1995 02:31:59 GMT
In article <444rka$56p@kira.cc.uakron.edu> David L Burkhead,
r3dlb1@dax.cc.uakron.edu writes:
>>1) were crocodiles always big?
>
Crocodylia today varies in size from the African Dwarf Crocodile (2 m) to
the Indopacific Saltwater crocodile, with unofficial records of 10 m.
Some lineages within Crocodylia occasionally got really big, esp. in the
Cretaceous and, in South America, the Pliocene. In the Tertiary and
Pleistocene of Africa, the largest crocs were comparable to modern
Crocodylus niloticus.
>>2) were there salt water crocodiles ?
>
All crocodylids (e.g. true crocodiles, as opposed to alligators or the
gharial) appear to have functional salt-excreting glands in their mouth.
They can thus tolerate saline water for a good length of time. In a
sense, all crocodylids are "salt water crocodiles." The Indopacific
saltie gets its name for a reason - it's been seen as far as 500 km from
shore - but the Nile and American crocs also regularly spend time in
seawater.
A previous poster asked about geographic distribution within a drainage.
True, crocodiles are generally not evenly distributed along a river.
They concentrate where the food is. Ever notice that the yearly
migrations of gnu always attract crowds of big niloticus? If their
distribution were spotty, but constant, sooner or later the gnu would
figure out where they could cross without being dragged in. As far as
anyone can tell, croc distribution will not be even, but neither will it
be consistent.
I suspect the rift lakes without crocs are that way because of waterfalls
rather than temperature. Crocs may not be endothermic, but they are very
good at regulating their body temperature through behavior.
This is cool - I had always hoped to bring such a discussion toward
truly advanced forms of life!
chris
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