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Re: The extinction of small dinosaurs



Someone wrote (I must have missed the original topic, so I only picked this
up from HP Bensen's e-mail):
>I can understand the effect of climate change, volcano activities and
asteroid hit etc causing the extinction of large sized dinosaurs but why it
also caused extinction of smaller dinosaurs, typically like maniraptoran
??<<
Remember that the extinction didn't just effect dinosaurs. Most marine life
was badly hurt, as were other forms of terrestrial life. So its not just a
question of "why were small dinosaurs affected too", its a question of "what
animals overall were affected and why?"
I think its easy to imagine why the oceans were so badly affected, since all
life in the oceans (with the exception of those freaky deep sea vent
creatures) depends on light. With the very base of the food chain ripped
away (microscopic photosynthesizing organisms), you would have pretty well
near complete collapse.
On land, of course, light is also essential for life as well. Without it,
plants can't photosynthesize, and will die. In terms of the K/T extinction,
you find that plants didn't fare too well. I am no expert on plants by any
means, but I would think that those groups most successful in coming through
the extinction were either lucky in placement (for some reason fallout/blast
effects weren't as bad, thinner dust layer), or have long germination
cycles/seeds can remain dormant until conditions are right (I know this is
the case for some types of conifers).
As for animals, you ask, why did small non-avian dinosaurs die out? Small
animals with high metabolisms need to eat a lot, simply because its
generally energy inefficient to be small and high energy. Surface to volume
ratios allow a high portion of heat to escape, and might metabolism=rapid
digestion of food, meaning you'll need to fill up that stomach sooner.
That's why if you have a pet rat/ferret/rabbit, etc., you'll see it eating a
lot: it needs to! I would imagine that the same was true for pre-K/T small
dinosaurs, that they would need to eat a lot. And dromeosaurs weren't
exactly small, but I think of them kinda like turkey-sized, and if you look
at your pet dog, it seems to either be eating or sleeping.
What does all this rambling mean? Well, by removing most photosynthesizing
plants from the biosphere, plus turning most non-saline standing bodies into
acidified lakes/ponds/etc. through the effects of acid rain from the debris
cloud (that which wasn't evaporated/boiled off during the initial
temperature spike), most herbivorous dinosaurs, large and small, will die
out fairly shortly. Of course, lots of the predatory/omnivorous animals will
have a field day, with the carrion, which would accumulate starting
immediately, and probably peek a week or two later, after most herbivores
had died. Then, of course, the carnivorous/omnivorous animals would be able
to feast on their compatriots for a while, but remember, its been suggested
that the dust lingered for months. I find it unlikely that a population
composed entirely of relatively rare carnivores to be able to survive off of
carrion from other carnivores for even a week. There simply wouldn't be
enough food in the ecosystem to support them.
So, what about what did survive, terrestrially, then? Well, mammals (though
not all of them, of course), crocodiles, turtles, amphibians, snakes,
lizards, and avians. Pretty odd grouping of metabolisms, and ecosystem
niches. But all modern representatives of these groups have something in
common; the ability to go into torpor (similar to hibernation). Crocodiles
can go at least 9 months without food. Amphibians can even be frozen solid,
and have all their vital functions cease, and still be unfrozen months later
and be perfectly fine. Birds and _some_ mammals both have the ability to
slow down their metabolisms (look at bears, for instance, as a famous
example), and lizards, snakes, and turtles can also subsist in lower than
normal metabolisms for extended periods, if the temperature and food supply
is low.
That is what I see as the common denominator for all the surviving
vertebrate groups: torpor. So why did small non-avian dinosaurs go extinct?
Well, I would say it was likely they couldn't go into torpor, and that's the
main reason. They succumbed to starvation and the aftereffects of the bolide
impact.
I roundly reject the "disease as mega-killer" hypothesis, because it would
be equivalent to a disease that killed all mammals. A) diseases aren't
successful from an evolutionary standpoint, if they kill all their
hosts...they'll die out B) No known disease has such a widespread effect
today. Even things like Ebola, which can be carried in other mammals
(closely related to us, I hasten to add), it isn't deadly to them. No doubt
when landbridges were opened, some diseases were carried across by the
immigrant dinosaurs, but I sincerely doubt that they ever decimated whole
species.
Anyways, sorry for typing so much. If you read down to here, you get a
cookie. ;) Its jus a subject that holds great interest for me, in terms of
its biological interactions, and its physical impacts.
Peace,
Rob

Student of Geology
400 E. McConnell Drive #11
Northern Arizona University
Flagstaff, Az. 86001
http://dinodomain.com
http://www.cafepress.com/robsdinos
AIM: TarryAGoat