What Caused the Pleistocene Extinctions?

The Pleistocene was known for having a variety of large-bodied animals throughout the world. All of a sudden, they disappeared. Today, we'll investigate the potential causes behind the extinctions.

Image Sources:
Paleoarqueiro
Mauricio Anton
WillemSVDMerwe
PaleoGuy
Beth zaiken

[animalorigins]

Hey everyone, so I’ve been informed that the image I’ve used for the giant koala was actually one of the giant koala lemur. That was an oversight on my part, apologies for that.

[cro-magnoncarol]

I remember seeing a study done on the La Brea Tar Pits that showed around the time of the megafaunal collapse their was an arid period & evidence of increased fires causing a floral turn over. This points towards humans not directly killing the megafauna but their use of fire changing the floral communities of regions they migrated to...

[mhdfrb]

TLDR; it’s a mess, but there are reasons to think humans were the decisive factor in the megafaunal extinctions (but at the same time, not the only significant factor).

The thing to note about the megafaunal extinctions is that even though they happened extremely recently and very quickly from an ecological or evolutionary perspective, they would still have occurred over hundreds or even thousands of years in human time. If you were someone who was alive at that time you’d not have realized it was happening.

And there are some things to note about climate:

- The “ice age” of the Late Pleistocene wasn’t continuous, but rather cyclical: the global climate was constantly cycling between glacial periods (ice ages) and interglacial periods (like the one we’re in right now). The end of the “ice age” was nothing more than this cycle repeating itself as it has done dozens of times before (which is why a lot of people instead refer to it as the end of the last ice age, to indicate that there have been dozens of ice ages during the Late Pleistocene and a corresponding number of warm periods as well). What this means is that the Late Pleistocene megafauna had lived through many of these cycles before without going extinct because of the climatic changes; not all of them survived for as long as the beginning of the current interglacial, but most of them did (and that’s also a list that includes the large animals we have today, almost all of which evolved during the Pleistocene and aren’t newly evolved animals that arose after the end of the last glacial period).

- not all the megafauna would have been affected by the end of the last ice age in the same way, because they didn’t all live in similar habitats like often assumed. A common pattern across the Late Pleistocene-backed up by the fossil record-is that during the glacial/ice age periods, grassland-specialized megafauna (mammoths, woolly rhinos, cave lions, etc) thrived while megafauna more suited to forested habitats (Smilodon fatalis, mastodons, most of the ground sloths, etc) actually declined in both population and range-because during an ice age, the expansion of glaciers removes a lot of water from the atmosphere so the global climate becomes drier, causing forests to die out and be replaced with grasslands. But when an interglacial arrives, we see the reverse pattern with grassland specialists declining (though usually without going extinct: again, megafauna as a whole survived repeated glacial-interglacial cycles) and forest-adapted megafauna increasing as the warmer climate led to increased rainfall in most places and thus more forest cover as a whole. If climate was the driving factor of megafaunal extinction, you’d expect it to favour one set of megafaunal species or the other (specifically, you’d expect only the grassland specialists to go extinct, since we’re talking about the megafaunal extinctions that happened around the end of the last ice age and start of the current interglacial), but instead we had megafauna die out regardless of their climate and habitat requirements.

- one caveat to this is the Australian megafaunal extinctions, which occurred earlier than in the Americas, and in two stages: the first stage happening slowly prior to human arrival and the second part happening more quickly once humans showed up around 40, 000 years ago (well before the start-let alone end-of the last ice age). This is because unlike the other continents and their cyclical climatic/habitat shifts during the course of the Pleistocene, Australia experienced a continuous change towards a drier climate. Most of the Australian megafauna were adapted for wetter, forested environments (though not all; many of the extinct short-faced kangaroos were well-adapted for arid desert habitats), and many of them went extinct, while others survived desertification thanks to areas that remained (and still remain) more heavily vegetated, especially in the more northern parts of Australia. These surviving megafaunal species, and the aforementioned desert-adapted megafauna, were then wiped out later when we showed up.

[indyreno]

Fun fact: the spectacled bear (Tremarctos ornatus) is the last living short-faced bear and the mernine or banded hare-wallaby (Lagostrophus fasciatus) is the last living short-faced kangaroo.

[alexv]

I appreciate the Touhou music starting at 7:40 (Beloved Tomboyish Girl, Cirno's theme from Embodiment of the Scarlet Devil)

[ileb]

Love your videos! Keep being awesome:)

[johnortmann]

There's a lot more to the human/fire interaction. When humans reached a new area, they took the fire regimen away from lightning (small, less-intense growing-season fires). Humans lit more fires during dormant seasons, which could be much larger and more intense. This would have altered and even destroyed entire ecosystems and replaced them with new ones, with profound effects on the creatures that inhabited them.

[veggieboyultimate]

Idk if you r working on a video but do you think you can do a video on plesiosaurs?

[HardCoreSciFi]

Megafauna commonly is cornerstone species of their biomes. Like, without mammoths, there could be no mammoth steppe. Thus, climate change might be not the additional reason for the Pleistocene extinctions, but the consequence of them - if multiple different biomes around the world are collapsing and changing because of the human-caused overkill.

[YetiUprising]

It was none of these hypotheses it was....



Aliens!

[SyIe]

👍⭐⭐⭐⭐⭐Finally a video about this. Great video!! many thanks for making such a great content!!❤❤

[jakobraahauge]

love your narration - American in the most charming, elegant, and pleasant way!

[DragonFae]

Here in Australia, there hasn't been any evidence of Aborigines hunting the megafauna. However, what there is evidence of is that the fire-stick farming they use caused a number of plant species to go extinct. Tests on the shells of Geniornus and emus from that era show that emus had a very generalized diet, whereas the Geniornus relied on a few specific plants, all of which went extinct around the same time as the megafauna.

[InternetDarkLord]

The problem with this speculation is that these extinctions may have been caused by many interconnected factors, and not all extinctions followed exactly the same combination.

[howardkerr]

Great video, I didn't hear you mention Rengal Island where Wooly Mammoth survived until around 5, 000 BC

[mugwugthemagnificful]

Why were the exceptions so similar in North America and Eurasia: Bison -Wisent, Moose-Elk, Brown Bear-Brown Bear, Wapiti(elk)- Red Deer, Gray Wolves- Gray Wolves. A lot of exceptions and they were pretty much the medium sized megafauna. A lot easier to kill.

[MR_Nosy_Otter]

basically in the end it was a combination of all the theories together depending on the area that lead to the extinction

[LucasSilva-kvkm]

love this chanel many thanks for making such a great content

[trentonbates]

That background music is underrated 😂😂

[charizardfan]

I appreciate the fact you used music from Diamond and Pearl in this