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RE: The extinction of small dinosaurs



BRIEF REPLY: Current research -- by J.R. Carey in
particular -- indicates extinctions are more complex
than simplistic scenarios of one asteroid impact.
Using bifurcation/evolutionary game theory, and
computer simulations of fast-slow dynamical systems,
an image is beginning to manifest itself: a
combination of factors (volcanoes, climates,
rising/falling sea levels and temperatures, the
asteroid, depleted gene pools, lethal diseases [the
opening of landbridges may have exposed breeding
populations to extinctions]) killed a wide array of
taxa. Some temperature-sensitive taxa (amphibians,
e.g.) survived for reasons unclear, although burrowing
may have played a part. Certain theropod clades
survived well beyond the events, outlasting even those
megataxa which lived in isolated areas in the early
Cenozoic. Today, ca. 9000 spp. of theropods exist, but
this is only part of the story. It may be decades
before a partially accurate picture of the events can
be sketched out.
*******************************************************
--- Daniel Bensen <dbensen@bowdoin.edu> wrote:
> >>I can understand the effect of climate change,
> volcano activities and 
> asteroid hit etc causing the extinction of large
> sized dinosaurs but why
> it 
> also caused extinction of smaller dinosaurs,
> typically like maniraptoran
> ??<<
> 
> It might help to define "small".  I remember hearing
> something like "all
> terrestrial animals over X kilograms were killed at
> the end-K", but I
> can't remember what the X was.
> 
> "Small" maniraptors like Troodon and Dromaeosaurus
> lived in Hell Creek
> right before the extinction, but those things were
> jackle-sized or
> bigger.  The size barrier may have been lower, like
> cat-sized and
> smaller, and it may have been that there just
> weren't any dinosaurs
> (aside from birds) that were that small at the time.
>  
> 
> Had the extinction occurred earlier, Compsognathus
> and kin might have
> made it through, but now that _is_ speculation.
> 
> Dan
> 
> 
> 


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