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Re: Dinosaur Extinction (Again)



Thom Holtz wrote, in response to one of my posts:

>Actually, the marine extinctions seem to make a lot of sense from the bottom
>of the food chain up.  There is massive extinction among the
>coccolithophorids (nanoscopic algae, whose calcareous shells make up the
>sort of limestone called "chalk"), although a few lineages survived.  The
>most conspicuous die offs among the macroinvertebrates are from probable
>planktonivores: ammonites (see work by Seilacher suggesting that these guys,
>unlike the nautiloid and coleoid cousins, were plankton-eaters), rudists,
>inoceramids (if any lived to the end of the Maastrichtian), etc.  At least
>some of the marine reptiles that died off, mosasaurs in particular, were in
>part ammonite eaters (evidenced by mosasaur bites on ammonites).

As a matter of fact, I agree with you! The kind of extinction scenario I am
prposing would _always_ start from the bottom up; there _would_ initially
be _massive_ casualties of _individuals_ at the bottom of the food chain.
However, given the vast numbers of individuals that would already have been
in existence, many of the major lineages of such organisms would likely
continue despite these massive losses. However, the further you go up the
food chain, the less individuals (and diversity of taxa) there are. So if
such taxa lost an equivalent or even a _lesser_ number of individuals (or
indeed species), a higher percentage of major lineages would likely become
completely extinct.

Witness that, despite their massive losses, some coccolithophorid lineages
nonetheless survived. _None_ of their major predators did, however.

Lee