I believe your story about population collapse. But what I find confusing: if the bison population had time to explode, why didn't bears and wolves also explode in number?
Especially given that a herd of bison would be more than capable of taking on a bear, like wolves, it would have to isolate an individual to escape unscathed.
Also: humans is my other guess - we have a well earned reputation for extirpating predators that compete with us.
Pronghorn tend to follow bison, only feeding after the bison have eaten the tall grass. This greatly reduces predation on pronghorn from ambush predators hiding in the grass; if they can see the predator with sufficient time, they are nearly impossible to run down.
And, there was an American cheetah? Welp, down a wikihole I go. Cheers!
Pronghorn are interesting animals and an evolutionary isolate. If science is to be believed, their closest living relative is the giraffe. North America used to have a wide range of very impressive predators that all disappeared around the last ice age. There was a strong selection pressure on the herbivores that were the food of these predators. While many of those predators are extinct now — American cheetah, dire wolf, saber-tooth tiger, et al — this has been a very recent change of circumstances in evolutionary terms.
To put it another way, bison and pronghorn had apex survival skills in an environment where many capable predators were hunting them at the same time. It is easy to forget that now because the set of top predators in North America has been dramatically reduced over the last several thousand years but these species didn’t evolve in the current environment.
It is never, ever "toward" anything. It is often "away".
Evolution is simply one static sorting event following another, on and on, with no gradual element towards something long-term. You only need variation in a population (same as in when a rock field includes various sizes of rocks but are otherwise similar), and the ability to inherit the properties of the parent.
Imagine a batch of bacteria, similar but slightly different from each other. One sorting event could be that someone applies some disinfection agent to the batch. Some bacteria die, some survive, and if that's because the survivors were slightly different then when they divide (as bacteria do) you suddenly have a lot more bacteria which handles the disinfection agent better than many of the previous generation. If someone re-adds the same disinfectant then again some die, some survive - presumably the ones which are better at it. Sometimes, but not always, that could be because of random mutations and "just" that one, existing in a subset, will fare better. And, if this continues, you end up with a batch of bacteria which doesn't really react much to that particular disinfectant at all.
But - the next day some other disinfectant may be applied. Now things change. Maybe completely different properties will fare better.
If you have a lot of different-sized rocks rolling down a mountain, and passing an area with holes - the smaller ones will fall down the holes, the larger ones pass - then you have the whole physical "law" of evolution, almost. You only need to add reproduction and inheritance to have biological evolution as we know it. And it's something that you just can't avoid. Which is why we have to fight antibiotic resistance all the time, and new Covid variants fare better than older ones - it's just sorting. Nothing gradual as such.
And, contrary to what anti-evolutionists claim, that to get a "new" functioning species, subspecies or variant, you need "an impossible number of just-so-happens-to-be-functional mutations" - no, it's not so. Dogs, for example, compared to the wolf ancestor of dogs, only have something like two major mutations: One for large size dogs (think Irish wolfhound) and one of very small dogs (think Chihuahua). The rest, e.g. the ability to digest lots of starch, which is present in many dogs, is simply that the genes for starch digestion came from wolves but were sorted for in dogs during domestication (i.e. it was easier for proto-dogs if they could actually survive on human foodstuff/leftovers/etc). So it became much more dominant than in wolves, which can't really for the most part get much out of starch unlike many (but not all) dogs.
Flight developed independently four times in dinosaurs alone, besides the pterosaurs. All the flying dinos relied on ancestral feathers.
I’m not here for that.
Now we know that the cheetah, dire wolf, saber-tooth cat, short-faced bear (bigger than grizzly), mastodon, mammoth, giant sloth, horses, camels, and other big animals were wiped out by a bolide strike, probably a broken-up comet. It set the whole hemisphere on fire, and left a layer of elevated-platinum dust under soot. No Clovis points are found above the charcoal layer.
So, not just "around the last ice age", but precisely 12,800 years ago. Somehow moose, bison, elk, and the smaller bears survived. And pronghorn, with nothing left that could catch them.
Are you talking about this?: https://en.wikipedia.org/wiki/Younger_Dryas_impact_hypothesi...
This does not seem to be a theory generally accepted by the scientific mainstream. There are competing theories for the Younger Drias extinctions that apparently have stronger evidence.
Among working geologists, there is no discussion about whether it happened, and only about how. A recent survey article is Sweatman,
The Younger Dryas impact hypothesis: Review of the impact evidence
https://www.sciencedirect.com/science/article/abs/pii/S00128...
The remaining controversy is how much the strike contributed to the Younger Dryas development and other coincident events, including extinctions.
Opponents have been disgracefully sloppy and disingenuous. Sweatman is very generous.
These scientific controversies are really fun to follow. In mathematics there's not as much drama! We barely have a handful of crackpot proofs of Riemann hypothesis per decade. (Except in theoretical computer science, thanks to the inestimable input of quantum computing people).
A valid proof of Riemann that fails to elucidate primes would face deep apathy, and would probably never be reviewed properly, rejected over spurious nitpicks. There might even be one.
https://www.sciencedirect.com/science/article/abs/pii/S00128...
https://en.wikipedia.org/wiki/Panthera
includes leopards and jaguars, usually seems they call them panthers if they're melanistic (dark hairdos).
by genetics, mountain lions are the biggest in the group that includes domestic cats.
https://en.wikipedia.org/wiki/Felinae
they purr and play and can domesticate so people do have them as pets, but of course are 70kg sized so a ton of money to feed and ton of space needed to play/exercise.