Cranial Ontogeny of the Extinct Dwarf Tapir Tapirus polkensis; with Comparison to that of the Extant Tapirus bairdii (Tapiridae, Perissodactyla)

Tapirus polkensis is the smallest known species of tapir to ever live, and the largest deposit of their fossils is currently located at the GFS in Gray, TN. Phylogenetics suggest that the extant T. bairdii may be the sister taxon to T. polkensis, although they differ greatly in their morphology. Variation exists among adult T. polkensis specimens, with patterns not present in T. bairdii. For this study, as series of 2D GMAs, with TPSs, were rendered on 10 skulls of T. polkensis and 48 skulls of T. bairdii, across both species’ ontogenetic series. Analyses confirmed that growth patterns of T. polkensis and T. bairdii are significantly different, including a telescoping effect seen only in T. bairdii, while patterns in T. polkensis depict a widening of the frontals, orbits, zygomas, and possible paedomorphism. While the phylogenetic positioning remains uncertain, this study provides morphological evidence to support a reexamination of those relationships.