CONICET | Buscador de Institutos y Recursos Humanos

The first studies on the endocranial cavities of extinct sloths date back to the nine- teenth century, but currently they are rapidly increasing in number thanks to the widespread availability of CT-scans and digital technologies. Today, highly detailed digital images of endocranial structures in and around the brain cavity, as well as the bony labyrinth and cranial sinuses, are relatively easy to reconstruct in a non- destructive way. The analyses published in the last decade have focused on the extant lineages and a few well-preserved, recently extinct taxa, though an increas- ingly larger number of fossil specimens are being considered. The rst comparisons among the taxa reconstructed so far (i.e. Bradypus, Choloepus, Catonyx, Glossotherium, and Megatherium) show that the observed morphologies can best be explained by phylogeny and only secondarily by paleobiological factors such as body size, locomotory modes, and possible feeding habits.The general form of the brain cavity appears to be conservative among sloths, with some peculiar characteristics in the olfactory bulbs, convolution pattern and cerebellum observed in Bradypus. In contrast, the morphology of the inner ear, and particularly that of the semicircular canals, appears different among the extant sloths Bradypus and Choloepus and the extinct giant sloths Glossotherium and Megatherium. Also, the pattern of cranial pneumatization appears to be driven pri- marily by phylogeny, and only secondarily related to body size. In the future, large-scale analyses of the morphology of the brain cavity, inner ear, and cranial sinuses can provide valuable, phylogenetically-informative characters and may be helpful in resolving the controversial phylogenetic relationships within Folivora. These same anatomical regions can also yield important functional insights and have the potential for elucidating the remarkable adaptations of extinct sloths.

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