A recent article published in Science (The emergence and demise of giant sloths), on May 22, 2025 looked into these uniquely American creatures that over a period of 30 million years occupied different ecological niches from grasslands, the Andes, and Alaska to Tierra del Fuego, and even one that was aquatic. They grew gigantic but now they are tiny and arboreal. Humans wiped them out when they reached the New World between 30 and 15 thousand years ago.
The article has some interesting data, and concludes that "size disparity increased during the late Cenozoic climatic cooling, but paleoclimatic changes do not explain the rapid extinction of ground sloths that started approximately 15,000 years ago. Their abrupt demise suggests human-driven factors in the decline and extinction of ground sloths."
The paper reported that giant-sized sloths (over 1 tonne in size) appeared independently three times: once among the Megatheroidea, and twice in the Mylodonoidea. The authors found that:
"The primary sloth extinction event began around 15,000 years ago, during the widespread expansion of Homo sapiens in the Americas between about 30,000 and 10,000 years ago. A second extinction event had occurred by the mid-Holocene, after humans arrived in the Caribbean islands, between 9000 and 5000 years ago). These two extinction events were substrate- and size-selective, preferentially targeting partially/fully terrestrial and medium/large-sized sloths
...
he selective extinction of large sloths led to a substantial reduction in the average body size and ecological disparity of the clade, reducing ecosystem complexity and functional richness. Small arboreal sloths likely survived on continents because they avoided extensive human impacts, such as predation, as they dwelt in denser, less-accessible habitats high in the canopy and have considerably reduced muscle mass for mammals of their size".
Size comparison sloths and human. Credits
The image above by Gabriel Ugueto depicts an extinct giant ground sloth (Eremotherium laurillardi) and an arboreal and extant one Bradypus variegatus (Three-toed Sloth), and a human being for size comparison. Look at those claws! Myths were surely creatied based on these giant animals.
Patagonian Monsters - Cryptozoology, Myths & legends in Patagonia Copyright 2009-2025 by Austin Whittall ©
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