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RE: The extinction of small dinosaurs


I've mentioned the ability to hibernate as a possible key to survival
through the K-T in many of my posts on extinction in the past.  (See
http://www.cmnh.org/dinoarch/2000Mar/msg00398.html where I not only
mention how far back I first began discussing hibernation, but also the
small size of the survivors).

I agree with most of your points in this post.

Allan Edels 

-----Original Message-----
From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu] On Behalf
Of Rob Gay
Sent: Tuesday, December 10, 2002 11:32 AM
To: Dinosaur Mailing List
Subject: Re: The extinction of small dinosaurs

Someone wrote (I must have missed the original topic, so I only picked
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
also caused extinction of smaller dinosaurs, typically like maniraptoran
Remember that the extinction didn't just effect dinosaurs. Most marine
was badly hurt, as were other forms of terrestrial life. So its not just
question of "why were small dinosaurs affected too", its a question of
animals overall were affected and why?"
I think its easy to imagine why the oceans were so badly affected, since
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
near complete collapse.
On land, of course, light is also essential for life as well. Without
plants can't photosynthesize, and will die. In terms of the K/T
you find that plants didn't fare too well. I am no expert on plants by
means, but I would think that those groups most successful in coming
the extinction were either lucky in placement (for some reason
effects weren't as bad, thinner dust layer), or have long germination
cycles/seeds can remain dormant until conditions are right (I know this
the case for some types of conifers).
As for animals, you ask, why did small non-avian dinosaurs die out?
animals with high metabolisms need to eat a lot, simply because its
generally energy inefficient to be small and high energy. Surface to
ratios allow a high portion of heat to escape, and might
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
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
at your pet dog, it seems to either be eating or sleeping.
What does all this rambling mean? Well, by removing most
plants from the biosphere, plus turning most non-saline standing bodies
acidified lakes/ponds/etc. through the effects of acid rain from the
cloud (that which wasn't evaporated/boiled off during the initial
temperature spike), most herbivorous dinosaurs, large and small, will
out fairly shortly. Of course, lots of the predatory/omnivorous animals
have a field day, with the carrion, which would accumulate starting
immediately, and probably peek a week or two later, after most
had died. Then, of course, the carnivorous/omnivorous animals would be
to feast on their compatriots for a while, but remember, its been
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
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).
can go at least 9 months without food. Amphibians can even be frozen
and have all their vital functions cease, and still be unfrozen months
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
normal metabolisms for extended periods, if the temperature and food
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
Well, I would say it was likely they couldn't go into torpor, and that's
main reason. They succumbed to starvation and the aftereffects of the
I roundly reject the "disease as mega-killer" hypothesis, because it
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
when landbridges were opened, some diseases were carried across by the
immigrant dinosaurs, but I sincerely doubt that they ever decimated
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
its biological interactions, and its physical impacts.

Student of Geology
400 E. McConnell Drive #11
Northern Arizona University
Flagstaff, Az. 86001
AIM: TarryAGoat