International Sloth Day- October 20

Written By: Aimee Turcotte
​Sloths: serene, sleepy, and slow. When Europeans discovered sloths in the late 15th and early 16th centuries, sloths were seen as unimpressive because of their slow movements and their perceived lack of motivation. In fact, sloths were named after the Middle English word slewthe or slouthe which means laziness [1]. The history of sloths goes back about 2.5 million years to 10,000 years ago during the Pleistocene epoch [2]. Sloths in the Pleistocene epoch could be found in the same grasslands, forests, mountain regions, tropical regions, and arid and semi-arid areas in South America as extinct animals. For instance, the extinct animals in these ecosystems include 1. The Terror Birds, a large extinct family of carnivorous flightless birds, 2. the Thylacosmilus, saber-toothed metatherian mammals, and 3. Glyptodonts, large armadillos.

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The Megatherium was the largest genus of Giant Ground Sloths and could reach 6 meters long and weigh 4 tons. It was unlikely that Giant Ground Sloths would be attacked by predators due to their size and their five 15-centimeter-long claws on each front paw [2]. Interestingly, Giant Ground Sloths had to walk with their feet turned inwards to protect their claws and themselves. The claws of Megatherium allowed these animals to dig paleoburrows, aka long and massive tunnels built for shelter and potential breeding. Some paleoburrows were 250 meters long, 2 meters tall, and 1 meter wide [2]! The claw marks of Giant Ground Sloths can be found in these paleoburrows today. It is unknown which species of Megatherium built paleoburrows, but it is predicted that one of the smaller species most likely made these tunnels. Once the Giant Ground Sloths became extinct, humans used their tunnels as shelter.

There is no clear evidence of how Giant Ground Sloths looked. Some scientists think that these sloths may have been furry, like the sloths we see today. However, some researchers believe that Megatheriums could not have been furry because, with fur, it would have been hard for them to keep cool in warmer temperatures. As a result, these animals could have been hairless like the giants of today such as elephants, rhinos, and hippos. Giant Ground Sloths, like today’s sloths, were herbivores, as proven by their fossils showing teeth shaped like those of herbivorous animals such as horses and cows. If necessary, Megatheriums may have added more protein to their diet by eating carrion, but there is no evidence of this. The tails of Giant Ground Sloths were large and may have been used for balance, suggesting that these animals occasionally stood on their hind legs to reach the top of trees [2].

The arrival of North American animals during the Great American Interchange and the growth of human populations led to increased competition for resources and habitat. This eventually led to the extinction of Giant Ground Sloths. Giant Ground Sloths were butchered by humans, which is evident in their fossils. However, Megatheriums were resilient against humans and other animals for a while, and a few even moved to North America. For example, a fossil of an Eremotherium, a close relative of the Giant Ground Sloths, was found in North Carolina [2].
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Currently, the closest living relative to Giant Ground Sloths is the Three-Toed Sloth. There are two living families of sloths: Two-Toed and Three-Toed. These families have received their names based on how many fingers a sloth has on their forelimbs. There are two Two-Toed Sloth species: Hoffmann’s Two-Fingered Sloth and Linnaeus’s Two-Fingered Sloth. Additionally, there are five species of Three-Fingered Sloths: Southern Maned, Pale Throated, Northern Maned, Pygmy, and Brown-Throated Sloths [1]. We have two Hoffmann’s Two-Toed Sloths here at Connecticut’s Beardsley Zoo named Rhubarb and Hope. You can find these sloths in the Rainforest Building. Rhubarb is a 34-year-old male and Hope is a 31-year-old female. Rhubarb arrived at the zoo in 2020, and Hope arrived in 1996.
Thank you for reading this blog, and I hope you enjoyed learning about sloths!

[1] https://slothconservation.org/sloth-o-pedia/ [2] https://www.youtube.com/watch?v=cE7itphjiZk&t=143s