Estimation of hearing capabilities of Early Miocene sloths (Mammalia, Xenarthra, Folivora) and palaeobiological implications

The Miocene Santacrucian sloths are a very important assemblage because they represent the first major radiation among sloths and, therefore, they could provide many insights about sloth evolution and diversity. Based on other studies, the hearing capabilities of Pleistocene sloths were identified. For a deeper understanding of these capabilities from an evolutionary point of view, in this article we study the hearing capabilities of Santacrucian sloths. We estimate the frequency range and the best frequency of hearing of six species of stem-megatherines and one species of mylodont. In most cases, the best frequency of hearing is much lower than the expected value for the estimated body mass of the species. This general shift towards low values of frequency is different than the pattern observed in mammals where sound localisation is improved by an increased sensitivity to high frequencies. In this article, we also propose some palaeobiological inferences of the low-frequency shift of hearing range in Mio...