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1. The bison is capable of defending itself against a tyrannosaur
2. The bison is capable of outrunning a tyrannosaur
3. The tyrannosaur did not prey on the bison
I'm not sure if I should comment, but I'll do it anyhow.
It is possible that the famed T-Rex might dine on bison. I find it odd that the more typical predator-prey relationships aren't mentioned. Is the wildebeast extinct due to the lion? Is the mosquito extinct due to the bat?
Bison in my grandfather's youth were quite numerous. When the herds combined during migration season, the resultant mass of the creatures spanned from horizon to horizon. I see no consideration that bison may have been too many to be eaten to extinction.
Neither do I see consideration of the common result of overpredation. Is it not possible for the numbers of prey creatures to be reduced to the point that their predators must find other food or starve? We know the dodo was an exception. If it wasn't, I don't think anyone would have ever much noticed the dodo.
Another possibility would be human intervention. Bison are the same kind of animal presently kept and protected by humans.
Neither would I dismiss your first hypothesis too quickly. Cattle of all kinds are prone to stampeding, and a creature as top-heavy as T-Rex, with so little capacity for gray matter could have a great deal of trouble keeping its balance if overrun. The wise Tyrannosaur might well choose not to take her chances around bison.
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The interaction between wolf and Deinonychus would be much more difficult to explain, however, if the competitive exclusion principle is to be upheld.
That's a new one to me, that "competitive exclusion principle". I suggest it might stand a better chance if you apply it to a critter less versatile than the wolf has proven to be.
It's a nice coincidence that just yesterday I saw an evolutionist show about polar bears and grizzlies. They're the same kind of animal, but the polar bear's diet is entirely different. Polar bears have become totally carnivorous, and they pass right by edible plant life because they're no longer aware they can eat it. There's more, but I think one can readily see my point: life is generally capable of surviving under a variety of conditions, and few creatures are restricted to a narrow diet. Pandas and koalas are the only two that come to mind, but maybe I've got bears on the brain.
I do not envy you the argument you've undertaken. I was going to suggest that scanty knowledge about the dinosaurs will make your task highly speculative and you might want to consider creatures we know about that compete for resources. Then I realized the ones we know about haven't driven each other extinct, so they're unsuitable.
I am keenly curious about the pre-flood world, so I can't say I'm sorry this topic came up. Of course I prefer ante-diluvian discussions to anti-diluvian, but one can't always be picky.
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