this post was submitted on 27 Jan 2024
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I don't ever remember hearing it suggested that dinosaurs were "sliding towards extinction" before the impact event.
I've always heard it WAS the impact that caused the extinction.
There were some theories about volcanism and other events that changed the environment enough to cause their decline, but from what I remember, most of those were proposed before we found the Yucatán crater.
Layman here, but as I recall there is a more recent theory that the evolution of flowering plants (130ish MYA) played a role in the decreasing diversity of the huge dinosaurs.
The usual evidence used for that is that the Triceratops like species seem to end up with just the one, and Trex appeared to be the only large predator in its ecosystems.
Although I understand there is new evidence suggesting that the North American Trex specimens found might be at least three different subspecies.
If I remember correctly, those two species were actually separated by millions of years.
Yes, that doesn't change my point. In both cases it looks like the ecosystem had multiple niches that in the fossil record previously having different species apparently all filled with a single species. With Trex, one of the current theories is that it filled different niches as it grew up.
Although with Trex, there may have been a half sized version that was hunting alongside the big one(s).