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Re: Cretaceous Mass Extinction
Why didn't they adapt that last time? Adaptive radiation doesn't
answer my 0uestion entirely.
Sorry I am a little late on this, but as the "mad photoperiod-extinction
theorist" I felt compelled to comment on this entry (which was quite
interesting, by the way!).
I feel that dinosaurs and the other organisms that suffered extinction
65 MYA simply did not have the time to adapt. Isn't that the key to
most selection in nature? If a sudden and catastrophic event takes
place, it is far more likely to cause mass extinctions then a gradual
change that gives organisms time to adapt.
Further, I will state again my belief that size was irrelevant to what
happened. Monitors, pythons, tortoises, crocodilians, sharks, rays,
etc. all grow to signifigant sizes yet were largely unaffected by the
mass extinction. Dinosaurs were selected against as a class because
they could not adapt to the sudden change in their environment, not
because of their size. Further, it is ironic that that most of the
large reptiles (by today's standards) mentioned above (with the
exception of some crocodilians) are tropical and completely incapable of
any sort of hibernation whatsoever. Any climatic-related theories to
the mass extinction must explain how the ancestors of these living
relics survived the hypothetical global cooling associated by an
asteroid impact. Also, if these ancestral forms survived in some
"protected" geographical range, then why didn't at least a few
representitives of the dinosauria survive with them?
It is nice to see people linking what happened in the seas at the time
with the terrestrial changes. Too often we overlook that the mass
extinctions in the seas were actually more terrific then those on land.
Lastly, the photoperiodic link is still hard to overlook in all of these
examples. Ferns coexist with angiosperms in cool, moist regions today
just as they did 65 MYA. There was a reason why the flowering plants
living side-by-side with ferns were selected against, while the ferns
were not. Physiological dependency upon seasonal changes in light
levels is the one common link that dinosaurs, angiosperms, corals,
sponges, bryozoans, etc. have in common, and it was this one factor that
was the primary cause of the Cretaceous mass extinction. Temperature
change just doesn't cut it (whether you believe dinos were endothermic
or not!), in my opinion. Catastrophic photoperiodic change is the