Análise morfométrica crânio-dentária tradicional e craniana geométrica do gênero Tapirus (Mammalia, Perissodactyla)

Abstract

Genus Tapirus is composed by perissodactyl ungulate mammals that belong to the clade Tapiromorpha (Haeckel 1866), to the superfamily Tapiroidea (Burnet 1830), to the family Tapiridae (Burnett 1830) and to genus Tapirus (Brisson 1762). This genus includes several fossil and five living species: Tapirus indicus (Desmarest 1819), the only Asian tapir; T. pinchaque (Roulin 1829), South American of the Andes Mountains; T. bairdii (Gill 1865), that lives in Central and northern South America; T. terrestris (Linnaeus 1758), which inhabits lowlands in northern South America, including Brazil (Brooks et al., 1997); and finally T. kabomani, which was recently described for the Amazon (Cozzuol et al. 2013). South American tapirs are North American imigrants from the Great American Biotic Interchange, that led to the formation of the Isthmus of Panama (Woodburne 2010; O’Dea et al. 2016). These animals reached their peak of diversity and geographic distribution during the Pleistocene (Holanda et al. 2011). Tapirs are herbivorous, feeding mainly on terrestrial and aquatic plants leaves, and fruits. Despite all the information available, evolutionary relationships among the species within the genus Tapirus are still uncertain. Recent works (Cozzuol et al. 2013, 2014) suggest that T. terrestris is a species complex. A better understanding of the evolutionary history of this clade is important to better support conservation strategies for the genus, which is key in the dynamics of tropical forests in Central and South America and southeast Asia, since tapirs are seed dispersers. Studies involving traditional cranio-dental morphometry and cranial geometric morphometry of the five living and fossil species of the genus Tapirus have never been done. For the analysis of Traditional Cranial Morphometry, 21 distance measures (n = 90) were analyzed using PCA multivariate statistical analysis method. The results showed that species are better discriminated when size is included in the PCA graphics, and only after larger species are removed shape has a greater diagnosis. The study of upper dentition variation under traditional morphometric analysis included 20 measures of distance (n = 70), followed by analyzes of variation of size and shape of the lower dentition, containing 17 distance measures (n = 113). Size is the variable that best separates the dentition of tapir species, since morphology is highly uniform between them. Lower m3 length is the dental character in lower dentition that better separates the species studied. Comparison between upper and lower dentition reveals that upper teeth are more diagnostic for the species studied. For the analysis of cranial geometric morphometry, landmarks are proposed for the study of tapir cranial shape through 2D geometric morphometric techniques, including 20 lateral cranial view (n = 71), 14 dorsal cranial view (n = 51) and 21 ventral cranial view landmarks (n = 44), followed by PCA multivariate statistical analysis. Lateral and dorsal view landmarks proved to be the most diagnostic for the species studied, providing interesting insights and trends on tapiroid cranial evolution. The shape of the forehead and the height of the sagittal / parassagital crests were the most diagnostic cranial characters for both traditional and geometric cranial morphometry analysis. Ventrally, the species analyzed do not differentiate significantly. The present work intends to add new information to the current cranial morphometric database of tapirs, which can help elucidating questions about the evolutionary history of tapirs.