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Re: Theories on the extinction of dinosaurs

On Fri, 12 Nov 1999, Seosamh wrote:

> I'm trying to define the problem more clearly. It's habitual <G>. I'm
> not a scientist, nor do I have any training in biology or earth  
> sciences. But I do have a preferred approach to problem solving.

Let me try to redefine it for you.  At, before, or some time after the
K/T, large, flightless non-crocodilian animals which layed eggs became
extinct. From that
time forward, this strategy appears (to me, at least) to have been
successful in only three biomes (grasslands, wetlands, and islands lacking
diversity in placental carnivores).  The principal limiting factor in
extant species is predation on eggs and hatchlings.  While it is very
difficult to do (fossil evidence is here again lacking) a case can be made
that similar pressures existed for large, flightless, egg layers
_throughout_ the Cenozoic.  If there is at least tentative support for the
above, it should follow that a reasonable suspect for dino extinctions is
predation.  The next question becomes: Did the composition of predatory
guilds change at the time of dinosaur extinctions?  In the only place
where we have a solid record of extinctions (North America), the answer to
that question is: maybe.  At the K/T at this location were badger-size
placentals (Cimolestes magnus).  And, following the extinctions, mammalian
radiation was so rapid and prolific that one can only conclude they were
in a sense poised to radiate (does anyone argue that a mid-cretaceous dino
extinction would have released such creativity?).  Indeed, a mere 400,000
years later, coyote-like predators existed.

Here, then, is a plausible smoking gun--especially since the same gun has
been linked (in the case of the entire Cenozoic) and proven (in the case
of extant oviparous species) to similar murders!  As with modern
extinctions, however, complex synergy between forces undoubtedly existed
at the K/T.  One possible scenario is that known K/T habitat fragmentation
facilitated edge predation (as seen in the Canadian Prairies today).
Another could be that large dinos in search of scarce K/T fodder were
pulled off there nests, enabling increased predation.  Another could be...