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Re: Dinosaur Extinction (Again)



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.

>> >Why won't the pattern of extinction be random?  I recall an
>> >article in Science News suggesting the pattern of extinction and
>> >survival at the K-T boundary was random.  (Sorry, I don't recall
>> >the attribution.)
>>
>> I've seen a few claims to this effect; suffice it to say I disagree with
>> them. I think that random extinctions would not extinguish many large taxa:
>> the chances of the odd species here and there all belonging to one
>> particular large taxon are statistically very slim. Besides, I would
>> _expect_ there to be a pattern.
>
>
>Again I challenge your assumptions.  Wouldn't the _expectation_
>for a pattern depend on the cause of the extinction event?  But
>more importantly, what does the evidence in the fossil record
>say?

I can't think of any known extinction mechanism that I believe would
produce a random pattern. Furthermore, while different causes would very
likely produce somewhat different patterns, the greater susceptibility of
taxa at the top of the food chain would in my opinion be a _constant_. The
variations would, I think, largely be in which _particular_ food chains are
the hardest hit.

Admitedly, however, while the above fits in with my perception of the
available data on various extinction events, my arguments here are largely
theoretical.

Lee