page_title: Lestodon
section_title: Cranial
hierarchical_section_title: Lestodon / Evolutionary adaptations / Cranial
caption_attribution_description: English: mounteed Lestodon armatus from Museo de La Plata
context_page_description: Lestodon is an extinct genus of megafaunal ground sloth from South America during the Pliocene to Pleistocene periods. Its fossil remains have been found in Argentina, Paraguay, Uruguay, Venezuela, Bolivia, and Brazil. Measuring approximately 4.6 metres from snout to tail tip, it is estimated to have weighed 2,590 kilograms. It was a herbivore and primarily fed on the grasses on the South American plains and is thought to perhaps have used its semi-bipedal stance to obtain foliage from trees. Lestodon is placed as member of the Mylodontidae as indicated by the lobed form of the last tooth in the dentition.
context_section_description: The skeleton morphologically reflects its evolutionary history as well as its daily activities. At the caudal end, the sloth’s head connects to its neck with a class one lever. The skull is two to three orders of magnitude larger than that of living species of sloth, but the muzzle itself shows highly positive allometry to the size of the skull in comparison to modern sloths and even other megafauna of the same order Pilosa.
  L. armatus had a large, blunt, and square mandible well adapted for foliage consumption. Its muzzle and dentition show a significant adaptation to this diet. The shape of the muzzle aided the ground sloth in the grazing necessary to sustain the metabolic activity of its large body; square, flat muzzles are associated with bulk feeders while pointed snouts are adaptive features of precision eaters, like the long sloping snout of modern anteaters, which are also in the same class Xenarthra (Bargo et al., 2006). The mandible, a class three lever, has a shape that indicates evolutionary pressure for strength over speed. To sustain its caloric needs with only plant matter, the sloth would have needed to be able to consume a high quantity of food with little precision.
  The species would dig for its food, and would have accidentally ingested a large amount of gritty dirt and soil particulate. This gives them a large crown height, called hypsodonty, that is unsuitable for strong bite forces. While the mandibular muscles would have been well developed to support the allometrically positive jaw of L. armatus, they would have also been extremely weak (Bargo et al., 2006).
caption: Mounted skeleton of Lestodon armatus on display at the Museo de La Plata
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