Order Pilosa includes the sloths (suborder Folivera) and the anteaters (suborder Vermilingua). Both were previously grouped as Order Xenarthra with the armadillos (now Order Cingulata), but it has been determined that similarities with armadillos are due to convergent evolution.
The pilosans are native to the Americas and especially flourished in South America when it was an isolated island during the Tertiary period. They diversified into some of the New World's most unique mammals, from extinct ground sloths the size of elephants to the highly specialized anteaters of today. There are ten living pilosan species plus three ground sloth species that went extinct recently enough to have coexisted with early Patagonian people.
Pilosans have some unique physiological traits compared to other mammals. They have extra bony "xenarthrales" between their lumbar vertebrae, a double vena cava vein bringing blood from the hindquarters to the heart, and retain primitive reproductive characteristics. Females have a divided uterus similar to the double uterus of marsupials and a combined urinary and genital duct, while males have internal testes with no glans to the penis. Pilosans also have remarkably reduced metabolisms compared to other mammals because they have specialized to eat low energy foods.
Anteaters have vestigial teeth with a weak, elongated mandible and a "worm-like" tongue which they use to feed on insects. Their tongue attaches to their sternum and can be extended up to half a meter. They walk with their feet turned up so that they tread on their knuckles or wrist in order to protect their curled digging claws.
Sloths spend most of their time hanging upside down while eating foliage, sleeping, mating, or even giving birth and may look like bundles of leaves themselves. In the Two-toed sloths, the fur is grooved to better grow two kinds of blue-green algae, giving them a greenish hue. The largest energy expenditure a sloth makes is to climb down to the ground once a week to defecate.
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- University of Michigan. (2014). Pilosa: Sloths and anteaters. Retrieved from the Animal Diversity Web website: http://animaldiversity.ummz.umich.edu/accounts/Pilosa/classification/
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