Comparative multivariate analysis of 3-D reconstructed encephalon in extant and fossil Folivora (Pilosa) and other representative Xenarthra

Abstract

ABSTRACT The Magnorder Xenarthra includes recent and fossil forms of Cingulata, Vermilingua, and Folivora. Folivora consist of extant and extinct sloths, presenting a great diversification in terms of size and habits. To analyse endocranial morphological variation in sloths, we measured digital endocrania of representatives of both fossil and extant Xenarthrans, and compiled measurements from the literature for a variety of mammals representing different orders, sizes, and habits. A Principal Component Analysis combining both datasets revealed a conservative covariance structure among mammalian orders, with the arrangement of scores along the first principal component summarising nearly 93% of morphometric variation, related in an almost isometric trend. A second analysis held only for endocranial measurements from Xenarthran endocrania, produced second and third principal components scores showing a variation trend among sloths related to relative dimensions of the olfactory bulb and the hypophysis. Interpolation of these scores also revealed an overlapping between Folivora and Vermilingua representatives and the separation of Cingulata, related to the dimensions of the olfactory bulbs. These results suggest that the endocranial structures exhibit a conservative pattern, varying according to the overall size of the encephalon, but also point to some convergence related to fossorial and arboreal habitat uses.