Giant sloths ruled South America — until hungry humans arrived


[dropcap]I[/dropcap]n a quiet corner of Bogota?, a giant ground sloth rears high above the glass exhibition cases to claw a stumpy tree. The fossil figure frozen in time is sentinel to a remarkable chapter of South American prehistory.

We now know these beasts best from Sid the Sloth in the Ice Age movies, an amiable klutz fast-tracked for extinction. But ground sloths like Eremotherium — the proper name for this beast depicted in Bogota?’s Museo Geolo?gico Jose? Royo y Go?mez — were no misfits.

Eremotherium’s kin roamed the New World for more than 20 million years munching vegetation, until a catastrophic encounter with a small but smart and voraciously hungry biped: homo sapiens. What followed next can be described as a great sloth slaughter or, more scientifically, as the Great Quaternary Extinction.

A fossilized skeleton of eremotherium towers at the Houston Museum of Natural Science. (Wikimedia)

In an astonishingly short span of a few thousand years, these giant beasts were eaten out of existence, survived only by smaller cousins like tree sloths and anteaters. Scientific research supports the theory that stone-age human hunters killed off these sloths soon after the hominid migration to South America around 20,000 years ago.

Along with giant sloths, a host of other fantastical megafauna disappeared: proto-horses (hippidion), two-tonne bears (arctotheria), rhinoceros-sized herbivores (toxodon), elephant-like mastodons, and armadillos the size of a saloon cars (glyptodont).

Also under threat was smilodon populator, a sabre-tooth tiger that preyed on the same large herbivores the hunters were wiping out. Weighing in at 400 kilos, with foot-long fangs, smilodon was the stuff of nightmares.

Its exit from the ecosystem probably came as a huge relief to the early humans who were double-locking their cave doors at night.

The Human Hunters

Still, it seems incredible that small bands of homo sapiens, hopscotching down the South American coast and using stone tools, could really kill off so many large animals. Hence there is considerable scientific debate whether this extinction event was caused by human overkill.

Other theories include climate changes, shifts in vegetation cover, shrinking habitat or — you guessed it — asteroid strikes. Or maybe it was a combination of all of the above. But somehow, it feels best to blame asteroids.

Unfortunately most evidence points to a bloody human hand in the demise of the ground sloth and its prehistoric friends.

A detailed scientific analysis published by the Royal Society in 2014 concluded that overkill was the “primary driver” of worldwide mega-fauna losses in the late Quaternary Period, particularly in South America, where the extinction was most severe and where there is no evidence of an asteroid or sudden climate change.

Where vegetation changes did take place, dietary studies show that giant sloths could switch from eating grass to shrubs or trees to keep pace. What they could not cope with was the sudden arrival of new neighbors on the block: The Sloth Slayers.

And a strange fact is that wild animals lack a flee response to humans until we start killing them over many generations. You can see this in remote islands of the Galapagos, where wildlife sits happily next to tourists or in Antarctica where you can literally pick up a penguin.

Migrating early humans arrived very late in the New World, and then stormed it like kids in a candy shop. Within a few centuries, they had spread to its most remote corners. The plodding mega-fauna, nai?ve to wily human ways, never knew what hit.

South America suffered the biggest extinction event, and lost a whopping 46 out of 58 genera of large mammals. Compare this to Africa, which lost just two out of 44.

African animals, such as elephants and giraffes, had evolved alongside human-like species for millions of years and learned to sense and evade hunters. This is why they have survived to today.

Africa still has many beasts over 1,000 kgs, and elephants as heavy as 6 tonnes, whereas the largest South American land mammal, the tapir, is a lightweight at 250 kgs.

But even if slow and nai?ve, South America’s giant sloths would have been a formidable adversary. Even small tree sloths are tough critters, as I found out picking one up from the middle of a busy road in southern Colombia.

I lifted it carefully by the wiry fur on its nape, but it could still twist its muscular torso and gouge my arms. Eventually I got this ingrate safely to the roadside jungle — but not without some bloody scratches.

Imagine my rescued tree sloth scaled up a thousand times and you have megatherium. The largest known ground sloth, it grew to 5 tonnes and 7 metres long, with body armoring made of bony plates under the skin and long claws that could fend off sabre-tooth tigers.

This is one sloth not to grab by the neck.

Other mega-fauna, like the more agile mastodons (similar to modern elephants with long tusks), would have been a bigger challenge to finish off despite teamwork and long-range weapons.

Searching for the Giant Sloths

In the end, none got away. Or did they?

The exact end-date for giant sloths is unclear. While most scientific texts state they were all snuffed out 10,000 years ago, it is a fact that smaller ground sloths were still roaming the Antilles Islands until just 4,000 years ago, shortly after humans arrived in canoes.

Colombian researchers T. van der Hammen and U.G. Correal dated bones and arrowhead remains from the Magdalena Valley to conclude that humans coexisted with giant sloths and mastodons just 5,000 years ago.

They also point to the “Elephant” statue in San Agustin dating from 3,000 years ago. Were San Agustin’s residents encountering the mastodon?

This raises an even more intriguing question: Could there still be megafauna living in remote rainforests? Fly in a plane over endless Amazon forest and it becomes almost believable. There are uncontacted human tribes down there. Why not out-of-touch sloths?

Cryptozoologists have been following rumours of giant sloth-like beasts from around South America for decades.

People of the remote Brazilian Amazon describe encounters with mapinguari, a 2-meter-tall mammal with bad hair, fierce claws, backward-facing feet, a horrible smell, and a terrible, shrieking cry. Similar beasts crashing around the forests of Bolivia are called jucucus.

Locals in southern Chile and Argentina have been reporting sloth-like mammals with bad body odor in remote mountain valleys for centuries. These yemisch, or lobo-toros (wolf-bulls), drew worldwide interest in 1895 when naturalists found what appeared to be the fresh hide of a mylodon ground sloth in a Patagonian cave.

The find sparked a rush of cryptid hunters including H. H. Prichard, a reporter from London’s Daily Express. Despite extensive searches, no mylodons were tracked down.

But the Cueva del Milido?n, near Puerto Natales in Chile, still had some mysteries to impart. In 1899, a deeper excavation by German palaeontologist Rudolph Hauthal turned up a layer of stone tools, sloth bones, hay, charcoal, plant fibers and sloth dung among what appeared to be the ruins of stone corrals.

He suggested that ancient humans had used the cave to stock captive ground sloths and maybe even domesticate them, a startling idea that became part of Patagonian lore, and the mylodon to be temporarily renamed Grypotherium domesticum, the domestic giant sloth.

Later studies showed these stone corrals to be natural rock-falls, and sloth bones dragged to the cave by large predators. Radiocarbon analysis of the sloth skin dates back 10,000 years, though it was well preserved by the cold cave air.

Anthropologists explain modern tales of mapinguari and yemisch as “folk memories” of megafauna hunts passed down through generations. That the campfire boasts of our sloth-slaying ancestors still echo today is in itself a small wonder.

Perhaps this explains our modern-day need to hunt lions with bows, fight bulls, throw darts in London pubs, or chase pixelated prey around our smartphones. As for the survival of mega-fauna, no biologist has been able to find hard evidence of a living specimen.

Not that this should stop you from looking.

To see sloths in Bogota?

For now, the surest place to spot our giant sloth is Bogota?’s Museo Geolo?gico Jose? Royo y Go?mez (Diagonal 53 N0. 34-53). The museum is open Monday to Friday, and admission is free.

For traces of Pliocene, travel to the Tatacoa Desert. Many of the desert campsites have fossils lying around and there is a quaint paleontological museum in Villavieja, a town one hour north of Neiva, the departmental capital of Huila.


  1. The ignominious legacy of mankind, and now modern society is accelerating the global mass extinction emergency. Every 24 hours, on average, 150 animal and plant species are being driven extinct while during this same time period the global human population increases by another 220.000.


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