Re: "Dinosaurs Died Within Hours After Asteroid Hit Earth..."

[Dann Pigdon <dannj@alphalink.com.au>]

Vlad Petnicki wrote:
> 
> To quote the Jeff Goldblum JP character "life will find
> a way".  Had there been significant number of dinosaur
> survivors of those first weeks, would not at least some
> of them had "found a way" like the surviving critters
> did?

Extinction isn't about animals dying (everything dies eventually) - it's
about them not being able to reproduce viably faster than the mortality
rate. Small animals tend to have shorter life cycles (which means they
can adapt more quickly), and are usually able to survive genetic bottle
necks better. Larger animals (in general) are more suceptible to
inbreeding. Hence a hundred elephants don't have a large enough gene
pool to survive as a species in the long term, whereas a hundred rats
can more or less take over the world.

Short life cycles may result in faster evolution, however they can also
be detrimental if unfavourable conditions persist for longer than the
individuals live. If a wild rodent only lives for a year or two, and
conditions become unsuitable for breeding for five years, then that
population becomes extinct. Not because adult animals aren't able to
survive, but simply because they can't reproduce successfully within
their lifespan. Large animals that live for several decades may not be
affected much by a mere five-year period in which they can not breed.

So there are both advantages and disadvantages to being small when
things get tough, and body size alone is not the deciding factor for
surviving an extinction event. Of course, small animals that live a long
time (and are generalists by nature) are the most likely to survive, but
the fact they are small is just one reason why they would do so.

-- 
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Dann Pigdon                   Australian Dinosaurs:
GIS / Archaeologist         http://www.geocities.com/dannsdinosaurs
Melbourne, Australia        http://www.alphalink.com.au/~dannj/
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