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Re: Impact only a part of it all....



In a message dated 98-08-08 00:25:54 EDT, dollan@cyberport.net writes:

<< But you are right indeed, why should nearly all of the large
 animals die out.  And, I suppose, it is really not just the large
 animals...there were still plenty of small dino species around, smaller
 than some crocodilians.  Why then should they have died out, but the
 Crocs didn't? >>

Large animals were simply bigger targets for the worldwide shower of ejecta
that resulted from the impact(!), not to mention the global fires (fed by a
significantly more oxygenated atmosphere than today's, I might add) and other
deadly hazards. Also, being large animals--top predators and herbivores--there
were fewer individuals alive at any one time, so complete eradication of a
species, to the last individual, was more likely. Mankind is proving every day
that it is far easier to kill >all< the tigers or >all< the elephants or all
the rhinos than it is to kill >all< the rats or >all< the cockroaches. It is
more difficult to destroy a widespread group of organisms comprising a
multitude of individuals than it is to destroy a group adapted to a narrow,
specific niche, comprising a smaller number of individuals. Mammals and small
herps were underfoot everywhere at the end of the Mesozoic, but dinosaurs
occupied only the higher, less populated niches. All the really small
dinosaurs by the end of the Cretaceous had become birds, and they did survive
the extinction. Any other dinosaurs of comparable small size had pretty much
been replaced by placental mammals by then.

Crocs? Maybe they were just lucky: A few individuals survived here and there
because they were holed up in a riverbank somewhere, out of reach. Crocs were
very diverse and abundant during the Mesozoic, but although they survived the
K-T event, they never again attained that level of diversity. We know of far
more extinct species than extant species of crocs, despite the big holes in
the fossil record.