Dinosaurs were probably not in decline before K-Pg

[Halichoeres]

At least in North America! This paper uses ecological niche modeling to estimate the habitats available to several dinosaur lineages. That means they estimated the environmental variables in places where Campanian and Maastrichtian dinosaurs were found, and then modeled where on the continent those same conditions might have prevailed, even if those areas wouldn't have been conducive to fossilization. They find no evidence of a decline in habitat, and suggest that any apparent decline is probably due to just having fewer available outcrops from the Maastrichtian.

This figure shows apparent habitable area based on known fossil-bearing outcrops, versus habitable area on the whole continent. Habitable area increases over time, rather than contracts, in the right panel.


Paper is open access: https://www.nature.com/articles/s41467-019-08997-2/

[suspsy]

Very interesting. I remember Jack Horner arguing back in the 90s' that dinosaurs were already on the verge of extinction before the asteroid hit. Looks like yet another one of his hypotheses has been shot down—although was he the one who originally proposed it?

[Gothmog the Baryonyx]

I thought that Titanosaurs in North America were on the decline, but that's about it. That's why is was such a devastating blow, it wasn't fininshing off a dying line, but wiped out most lines of a very successful group. (Well, more than one of course, of course with pterosaurs, plesiosaurs etc...) I'd heard the Horner theory before, it's one of those things people on the internet take as fact for some reason?

[Tyto_Theropod]

Perhaps because it fits with the popular identification of 'dinosaur' with something ancient and invalid at best and unfit and maladapted at worst. Of course, nothing could be further from the truth when considering what was - and indeed still is - one of the most successful and diverse vertebrate groups on the planet. The K-Pg event was truly a tragedy, but on the other hand, had it not happened I would likely not be here typing this. It's a very poignant thought.

[stargatedalek]

There is still the next question though, no they weren't on the verge of extinction, but had they become under-diversified as was also often suggested alongside that? Did this reliance on generalization end up being their downfall while both smaller and more specialized animals survived? Or perhaps that meant were they reliant on extremely large populations to survive?

[Halichoeres]

Like so many questions in paleontology, the answer might just be "sampling bias."

[Shonisaurus]

I think it is one of the great mysteries of the history of paleontology to know what was the cause of the disappearance of dinosaurs and other prehistoric animals of his. No response from scientists I understand in my ignorance is enough to convince me. It is one of the great mysteries of science like so many others.