Cranial Geometric Morphometric Analysis of the Genus Tapirus (Mammalia, Perissodactyla)

Abstract

Tapirs are perissodactyl ungulates of the genus Tapirus. The family Tapiridae was more diverse in the past. Genus Tapirus include five living species: T. indicus, T. pinchaque, T. bairdii, T. terrestris, and T. kabomani. Despite all the information available about tapirs, evolutionary relationships among species within the genus are still uncertain. Recent works suggest that T. terrestris may be a species complex. A better understanding of the evolutionary history of this clade is essential to better support conservation strategies for the species of this genus, which are keys in the dynamics of tropical forests in Southeast Asia and Central and South America. Geometric morphometry has been proved to be a useful tool for the study of morphological evolution in mammals, but studies involving cranial geometric morphometry of tapiroids have never been done. We hereby propose landmarks for the study of tapir cranial shape through 2D geometric morphometric technique, including 20 in lateral cranial view (n = 71), 14 in dorsal cranial view (n = 51), and 21 in ventral cranial view (n = 44), followed by PCA multivariate statistical analysis that ordinated specimens from each of the three data groups along the major axis of shape variation. Lateral and dorsal view landmarks proved to be the most diagnostic for the species studied, providing interesting insights and trends on tapiroid cranial evolution. Ventrally, the species analyzed do not differentiate significantly. In this paper, we add new information to the current cranial morphometric database of tapirs, which can help elucidate questions about their evolutionary history.