Eight-mile frieze of Ice Age beasts found in Amazon rainforest (2020)

"While genus Equus, of which the horse is a member, originally evolved in North America, these horse relatives became extinct on the continent approximately 8,000–12,000 years ago. In 1493, on Christopher Columbus' second voyage to the Americas, Spanish horses, representing E. caballus, were brought back to North America, first to the Virgin Islands; they were introduced to the continental mainland by Hernán Cortés in 1519. From early Spanish imports to Mexico and Florida, horses moved north, supplemented by later imports to the east and west coasts brought by British, French, and other European colonists. Native peoples of the Americas quickly obtained horses and developed their own horse culture.[5][6]"

Source: https://en.wikipedia.org/wiki/Horses_in_the_United_States

Firstly, your linked paper is focused on North America, so we can't say it's also applicable to, say, the extinctions of Homo floresiensis and Stegodon florensis insularis that correlate rather well with the arrival of modern humans.

Secondly, it repeatedly refers to global _cooling_ through the Younger Dryas Event. Just to clarify.

And tbh, claiming the overkill/big black hole hypothesis is merely current fashion is overly simplistic. It was described in the 60s based on available data, and hey, we're getting better data now, so yay, science is incorporating new data, like we expect.

And I'll note that the data points for human predation of megafauna used in that paper are likely to change also with time, so who knows how correct that paper's conclusions will be in another 20 years?

I don't see why "it was probably both" shouldn't be the default position. We know humans hunted megafauna, but like the fossil record, we know that only some evidence will be preserved, and only some of that evidence has been found.

But logically, both environmental change and the introduction of a novel predator (and other novel predators that predator may have brought with them) are bad for populations of species which a low replacement rate.

Kākāpō are a very good example. Human settlement brought habitat loss, causing their numbers to decline, and their breeding success rates to drop (and they were slow breeders to start with) as the more clement habitat was modified by humans, thus pushing them into areas with lower productivity.

But what ultimately pushed them to nearly going extinct was the introduction of very effective mammalian predators (mustelids). They had evolved for a land where the only predators were avian and sight based. So they became flightless because no point in flying away from danger when the danger was flying above you, and they developed cryptic colouration, they'd freeze when they sensed danger and became nocturnal. And most importantly, they used scent in lieu of dramatic colours to find each other in dense forest in the breeding season. No harm there, because raptors hunt by sight, not scent.

But being a smelly bird who is camouflaged and nocturnal and stands still, is no defense against ground predators who hunt by scent and quite appreciate not having to run after you.

I have the diaries of an explorer in the 1890s who would eat five kākāpō for breakfast, they were that easy for him to locate using his dogs, within 80 years of his parrot based breakfasts they were extinct on the mainland.

But yeah, habitat loss reduced their range, then human hunting reduced their range, then feral dogs and later cats reduced their range. But they were still around in decent numbers.

Then mustelids were introduced, and that was the tipping point, but only in the context of the prior stresses.

So for megafauna, hunting pressure places a population under stress, especially in species with a low replacement rate.

Climate change and the resulting changes in the ecosystem also puts populations under stress.

Maybe one of those stressors was survivable, but probably not both.

And for some megafaunal extinctions, especially on islands, it's pretty obvious humans were the deciding factor. Maybe not through hunting, just habitat loss could be sufficient (e.g., elephant bird), but often habitat loss went hand in hand with intensive hunting (e.g., moa)

This paper's worth a read. https://www.academia.edu/2644492/The_Associational_Critique_...

Do you know when the megafauna of Madagascar went extinct? Right around the arrival of humans. What about New Zealand? Shortly after the arrival of humans. In every historical, known example of human introduction to a new ecosystem, most animals over 50lbs get eaten.

And you start to see the problem here...