Harpy eagle kill sample provides insights into the mandibular ontogenetic patterns of two-toed sloths (Xenarthra: Choloepus)

Abstract

Skeletal ontogeny of xenarthrans is poorly known, especially because of the paucity of study specimens from distinct developmental stages. Here, we investigate morphometric aspects of the mandible ontogeny in the two-toed sloths, Choloepus spp. We examined mandibles of infant, juveniles and subadult sloths that were present in kill assemblages of harpy eagles, Harpia harpyja, and complemented our study with adult museum specimens. We carried out uni- and multivariate linear morphometric analyzes to assess the growth pattern of the mandible. Harpy eagles did not prey on adult two-toed sloths, preferring younger individuals. We found an overall strong correlation between the total length of the mandible and other mandibular measurements across age classes, with some of them scaling isometrically, and others presenting allometric growth. Also, morphometric data correlated with patterns of symphysial fusion across ontogenetic stages, rendering the latter a reliable indicator of the animal’s age category. Although it was necessary to complement our sample with museum material, individuals obtained from the harpy eagle kill assemblage proved to be a valuable complementary source of specimens to be studied.