Exploring the Extinction of Megafauna

The Museum's great standing skeleton is Mammuthus, the mammoth, which lived about 11,000 years ago.
D. Finnin/© AMNH

The American Museum of Natural History is world famous for its vertebrate paleontology halls, where the story of vertebrate life is traced from its beginnings to the near present, as told by the most direct form of evidence we have: the fossils themselves.

In the Lila Acheson Wallace Wing of Mammals and Their Extinct Relatives visitors marvel at mounted skeletons of vanished beasts, prodigious in number and variety. Many of the species seem quite familiar, not only because of frequent cameos in movies, but also because they have reasonably close living relatives.

Australia's extinct marsupial "tapir" Palorchestes azael died out about 40,000 years ago.
© 2019 by Peter Schouten

At one end of the wing are a Columbian mammoth  and an American mastodon. Both are very definitely proboscidean, or elephantlike, in body form, although their last common ancestor lived about 25 million years ago. On the North American mainland, populations of mammoths and mastodons were still living as recently as 12,000 years ago; all were gone 1,000 or so years later. A couple of island-bound groups of woolly mammoths struggled on, but these too had disappeared by 4,200 years ago. Asian and African elephants persisted. These magnificent beasts didn’t. Why?

The largest of the giant ground sloths, Megatherium americanum, may have weighed as much as 2,000 kg–4,000 kg (4,400–8,800 lb). 
© 2019 by Peter Schouten

Elsewhere in the hall are members of Xenarthra, today an almost exclusively South American group that includes living armadillos, tree sloths, and anteaters. The largest of the living xenarthrans is the giant anteater (Myrmecophaga tridactyla), but as late as 12,000 to 13,000 years ago there were several much larger xenarthran species in both North and South America that may have weighed as much as 2,000–4,000 kg. Among these was gigantic Lestodon, whose closest living relatives, the two-and three-toed tree sloths Choloepus and Bradypus, weigh no more than 5 kg. They made it, Lestodon didn’t. Why?

Giant ground sloths such as Lestodon lived in South America and became extinct 30,000 years ago. 
D. Finnin/© AMNH

Many other Quaternary species prospered in their native environments for hundreds of thousands of years or more without suffering any imperiling losses. But beginning about 50,000 years ago, something started happening to large animals. Species sometimes disappeared singly, at other times in droves. Size must have mattered, because their smaller close relatives mostly weathered the extinction storm and are still with us.

So why did these megafaunal extinctions occur?

A short but honest reply would be that there is no satisfactory answer—not yet. The debate continues as fresh leads are traced and dead ends abandoned or refashioned in order to accommodate new evidence. It’s a great time to be a Quaternary paleontologist!

Adapted from End of the Megafauna: The Fate of the World’s Hugest, Fiercest, and Strangest Animals by Ross D. E. MacPhee with illustrations by Peter Schouten. © 2019 by Ross D. E. MacPhee. Illustrations copyright © 2019 by Peter Schouten. Used with permission of the publisher, W.W. Norton & Company, Inc. All rights reserved.