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Re: what killed choristoderes?
Ken Kinman wrote:
Does anyone have any ideas what killed off the choristoderes
(champsosaurs) in the Eocene (or Oligocene?)?
The youngest record for the Choristodera is Oligocene (the
appropriately-named _Lazarussuchus_). The oldest record AFAIK may be the
poorly known _Pachystropheus_ from the Late Triassic. More definite records
of champsosaurs are of Middle Jurassic age.
easily killed off, since they made it through the K/T extinction (perhaps
due to a similar aquatic habitat that also protected the surviving crocs).
And, like crocs, they remained remarkably conservative through their long
evolutionary history (apart from one or two oddballs, like the long-necked
Japanese critter _Shokawa_).
It seems likely to me that the crocs just crowded them out, either by
competition (perhaps for habitat, such as for nesting sites), or big crocs
acquired a taste for choristodere eggs or young (and just ate them into
The choristoderans were remarkably gavial-like (although at least a few
mimic the placodonts), so possibly it was competition with crocs that wiped
them out. (Like competition with the radiating rodents has been suggested
as a reason for the extinction of the multituberculates.) I've also heard
the extinction of the choristoderes may have something to do with the
radiation of the Cetacea, again because of niche competition. With such a
spotty fossil record (they just come and go like summer clouds) and enormous
ghost lineages it's impossible to gauge if the extinction of the
champsosaurs was the culmination of a decline or not.
Unless the extinction of a group is sudden and worldwide (and sometimes not
even then) it is generally very difficult to figure out why some groups die
off and others prevail. For why some groups survive mass-extinctions and
others don't, I like Steven Jay Gould's idea that sometimes it's just dumb
P.S. And now for something completely different. I've been asked politely
by a few list members for a please-explain for my elephant joke. (Why do
elephants have Big Ears? Because Noddy wouldn't pay the ransom). Here
Noddy was a little elvin boy created by author Enid Blyton, who wrote a
series of delightful children's books centering around the adventures of
Noddy in his home town of Toyland. Noddy's best friend was a fellow elf
named Big Ears. (Hence the joke.) The books were very popular in Britain
and Australia, and I've seen them in the U.S., but I don't believe they
really took off here.
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