Paleobiology of the Santacrucian sloths and anteaters (Xenarthra, Pilosa)

BARGO, M. S.; TOLEDO, N.; VIZCAÍNO, S. F.

Early Miocene Paleobiology in Patagonia: High-Latitude Paleocommunities of the Santa Cruz Formation

Cambrigde University Press

Lugar: Cambridge; Año: 2012; p. 216 - 242

This chapter reviews the paleobiology of pilosans (anteaters and sloths) from the Santa Cruz Formation, which comprise at least one genus of vermilinguan and 11 genera of sloths. Paleobiological studies performed on these xenarthrans include: estimation of body mass (through multivariate regression); analysis of the limbs (through morphometric and qualitative-comparative morphofunctional analyses) so as to infer the locomotor habits and substrate use, and studies of the masticatory apparatus (mainly through analysis of tooth morphology and wear facets, plus the anatomy of the masticatory apparatus as a whole), to infer probable feeding habits. The Santacrucian anteaters were small animals, about six kg, well suited for climbing and for scratch-digging the substrate in searching for its preferred food, social insects. Various sloths were moderately large-sized forms, the largest reaching about 100 kg, with a locomotor pattern distinct than that of living sloths, resembling more that of vermilinguans and pangolins. The results suggest well-developed digging capabilities, but semiarboreal habits cannot be ruled out. Megatherioid sloths were most likely leaf eaters, and the primary method of food reduction must have been by shearing or cutting (with a predominance of orthal movements). Mylodontid masticatory movements included a larger transverse component, and food reduction must have been by crushing and grinding, which suggests they fed on more compact, three dimensional and fibrous food items like plant underground storage organs. The semiarboreal habits suggested for anteaters and probably sloths indicate the nearby presence of forested areas. The specialized feeding habits of vermilinguans are indicative of tropical and warm temperate environments because they would have depended on a year-around availability of social insects. The feeding habits of sloths are also consistent with forests, although they do not preclude the existence of open environments.