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Re: Dinosaur Extinction (Again)

At 01:47 PM 11/22/96 -0500, Lee McLean wrote:

>Andrew Robinson wrote:
>>I understand the argument that says animals at the top of the
>>food chain SHOULD be the first to go.  There are fewer of them
>>and they are more dependent on the animals below than vice-versa.
>>My question is, is there evidence in the fossil record or in
>>ecological studies to support this argument?
>The way I read the K-T extinction, that's exactly what happened. The dinos
>were at the top in their biome, and they went. The sea reptiles were at the
>top in their biome, and they went. The pterosaurs were at the top in their
>biome, and they went. And so it continues on down the food chain. The most
>successful taxa were the hardest hit, the least successful the least
>hardest. And the K-T event isn't the only major extinction event in which I
>observe this pattern.

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).

Not to say that this is necessarily the only thing happening in the seas at
the time, but that the extinct was not necessarily top-down.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661

"To trace that life in its manifold changes through past ages to the present
is a ... difficult task, but one from which modern science does not shrink.
In this wide field, every earnest effort will meet with some degree of
success; every year will add new and important facts; and every generation
will bring to light some law, in accordance with which ancient life has been
changed into life as we see it around us to-day."
        --O.C. Marsh, Vice Presidential Address, AAAS, August 30, 1877