“All hail the Great Beast Megatherium!”

File:Megatherium NT small.jpg - Wikimedia Commons
A reconstruction of the Great Beast
Image Credit: Nobu Tamura, (© N. Tamura), http://spinops.blogspot.com/2015/02/megatherium-americanum.html

“Deluded! Madman! Fake Scientist!”

The Cryptozoologist had been called these a lot throughout his professional career, (as well as other, more mean things). Time after time after time he had failed to discover any of the amazing creatures’ people claimed to have seen, with the majority being proven to never have existed in the first place. Now, nearing his retirement, he was wandering the amazon rainforest looking for yet another cryptid; the “Mapinguari”. “Just turn around” the voice in his head said (not for the first time). “They’re just stories made up to attract tourists or hoaxers trying to make a name for themselves or misidentified animals. None of them are real!”. The Cryptozoologist sighed, and for the first time in his life he wondered “Maybe I am a crazy old man”. Then he heard it, a crash of vegetation coming from the trees just to the left of him. He turned round, straining to locate exactly where the noise had come from. Then he saw it, and his jaw dropped. What he was seeing was an animal believed to have gone extinct 8,000 years ago. It was a great beast taller than an elephant and just as bulky, which possessed huge claws that it was currently using to pull down branches from a nearby tree towards its mouth. As he took out his camera and frantically took pictures two more large adults shuffled out of the forest, one of which had a baby clinging onto to its back. “They wouldn’t believe me” the Cryptozoologist thought. “But just wait till they see you!”

This “Great Beast” is known scientifically as Megatherium Americanum (meaning “Great Beast from the Americas”). Megatherium is an animal that palaeontologists have known about for a very long time. The first fossils were discovered in 1787, four decades before the first dinosaurs would be found, in Argentina by a man named Manuel Torres. After their discovery these bones were shipped to the Museo Nacional de Ciencias in Madrid, Spain, where they still reside today (another reason to visit Spain!). It was from these bones that French naturalist Georges Cuvier first described and named Megatherium, noting its close relation to modern day tree sloths. After these first fossils more were discovered, including bones found by Charles Darwin from 1832-1833 during the first Beagle expedition. Even nowadays new discoveries are revealing more insights. For example a paper published in 2017 (by Bocherens et. al.) looked at preserved collagen proteins in Megatherium fossils to give insights into its diet. Some people have gone a step further and claimed that Megatherium is still alive somewhere in South America. Stories from Brazil tell of the “Mapinguari” or “sloth monster”; a shaman who was transformed by the gods into a giant sloth-like creature. Cryptozoologists (like the one in the story) think the Mapinguari is actually a late surviving species of Megatherium, however scientists (and yours truly) don’t take these stories seriously due to absence of any concrete evidence.

A mounted skeleton of Megatherium with a awe inspired human for scale!
Image Credit: Beatrice Murch, https://www.flickr.com/photos/blmurch/3495336846

Megatherium belonged to a large order (or “superorder”) of mammals known as the xenarthans. Modern xenarthans include Tree Sloths, Anteaters & Armadillos, but during the Cenozoic era this group was much more diverse. From their origins in South America they ended up colonising North America, grew to a range of shapes and sizes and occupied a wide variety of habitats ranging from the treetops (e.g. modern tree sloths) to even the ocean (e.g. the swimming ground sloth Thalassocnus). Megatherium itself belonged to a sub-order of xenarthans commonly known as the “Giant Ground Sloths”. These sloths were very different from their slow moving and tree dwelling modern counterparts. They were bulky, ground living herbivores with large and sharp claws. While Megatherium itself was confined to South America other species of Giant Ground Sloths migrated across the Isthmus of Panama into Central and North America. This was during the great American interchange; a time where multiple species from South America migrated into North America (and vice-versa). As a result Giant Ground Sloths established populations in places such as Costa Rica, Texas and California.

Because multiple fossils of the “Great Beast” have been known to palaeontologists for some time we have a pretty good idea of what it would have been like. Megatherium roamed the South American pampas, mostly in Argentina, Bolivia and Uruguay, from the Pleistocene (roughly 400,000 years ago) to Early Holocene (roughly 8,000 years ago) periods of the Cenozoic era (a timespan commonly known as the “Ice Age”). This beast stood over 3.5 metres tall when fully upright and weighed up to 4 tonnes, making it the largest animal in South America during the Ice Age and the largest xenarthan ever. Its potbellied frame was supported by column-like hind legs that would have given it a long reach. Furthermore preserved Megatherium track-ways and its skeletal anatomy indicate that it could have walked on two legs as well as on all fours. Its front limbs were tipped with large, non-retractable claws which were used for pulling branches closer to them to eat and for digging up roots and tubers. In fact the claws were a reason that Megatherium was initially thought to have been a burrower, living like giant mole! Big claws would have undoubtedly been very effective defensive weapons with Megatherium using them, alongside its large size, to protect itself from predators, such as the large Sabre-Tooth Cat Smilodon populator. Other distinctive features include a relatively narrow snout, a prehensile upper lip (like a black rhino) and a thick shaggy coat. This coat is found on most Megatherium reconstructions and is based on the discovery of exceptionally preserved hair and hide specimens of related Giant Ground Sloths. However a study from 2002 (Fariña 2002) has speculated that Megatherium might’ve been nearly hairless! This is based on the observation that modern large mammals, such as elephants and rhinos, are mostly hairless to prevent them from overheating in hot climates (large animals produce a lot more excess heat). Megatherium may seem very different to what we would think of a typical large herbivore today. However the overall body plan of a large, bulky, bipedal herbivore with large claws has actually appeared a few times throughout earth’s history. One example is the Therizinosaur dinosaurs; a group which lived a full 65 million years earlier than Megatherium but is thought to have lived a similar lifestyle. This is an example of convergent evolution; where two completely unrelated organisms, often separated by millions of years of evolution, evolve similar body plans to live in similar ways. It’s a very fascinating phenomenon that has resulted in a lot of symmetry between modern and extinct animals (e.g. Dolphins and Ichthyosaurs).

A Megatherium looking at the horizon as two glyptodonts waddle by!
Image Credit: D. Bogdanov (DiBgd), https://commons.m.wikimedia.org/wiki/File:Pleistocene_SA.jpg#mw-jump-to-license

Such a majestic animal is another example how diverse the megafauna were during the last Ice Age. However the majority of these animals are not around anymore. Megatherium’s story is similar to other megafauna. Climate change at the end of the last Ice Age played a part, resulting in a loss of habitat and decline in population. This was combined with the arrival of modern humans into South America roughly 14,500 years ago. Some Megatherium bones bear distinct marks on them that indicate that they were cut by human tools. Furthermore other bones have been unearthed alongside human made stone tools and weapons. Tools, high intelligence and co-operation made humans a terrifying predator for a Megatherium to try and defend itself against and humans were so efficient that Megatherium numbers dwindled further. Eventually the dynasty of the Great Beast would come to a close 8,000 years ago. This unfortunate end makes one wish that the Cryptozoologists were right, and that Megatherium was somehow still living in South America to this day. If this were the case then I’m sure many more people would see what a “Great Beast” it really was.

References/Further Reading

Bocherens et. al. 2017 paper reconstructing the diet of Megatherium from analysis of collagen in the fossils

Bocherens et. al. (2017), Isotopic insight on paleodiet of extinct Pleistocene megafaunal Xenarthrans from Argentina. Gondwana Research, 2017; 48: 7 DOI: 10.1016/j.gr.2017.04.003

Billet et. al. 1997 paper examining the inner ear anatomy of Megatherium and what it tells us about its body mass and agility

Billet, G et al. “The inner ear of Megatherium and the evolution of the vestibular system in sloths.” Journal of anatomy vol. 223,6 (2013): 557-67. doi:10.1111/joa.12114

Natural History Museum website article profiling Megatherium and detailing a project that was digitally scanning all the fossils Charles Darwin collected on the 1831-1836 Beagle voyage

Brewer, Pip, “What was Megatherium?”, Natural History Museum, https://www.nhm.ac.uk/discover/what-was-megatherium.html

Fariña 2002 paper suggesting that the largest Giant Ground Sloths, such as Megatherium, were mostly hairless

Fariña, Richard. (2002). Megatherium, the hairless: appearance of the great Quaternary sloths (Mammalia;Xenarthra). AMEGHINIANA. 39. 241-244.

Politis et. al. 2019 paper, published in Sciences Advances, on the discovery of Megatherium remains that show evidence of Human Hunting

Politis, Gustavo & Messineo, Pablo & Stafford Jr, Thomas & Lindsey, Emily. (2019). Campo Laborde: A Late Pleistocene giant ground sloth kill and butchering site in the Pampas. Science Advances. 5. eaau4546. 10.1126/sciadv.aau4546.

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