Dental characters of the Quaternary tapirs in China, their significance in classification and phylogenetic assessment

Most of the Quaternary tapir fossils from China are isolated teeth. The purpose of this paper is to identify them and to extract systematic and evolutionary information from them. Based on morphology and W/L ratio, isolated teeth can be identified successfully. On the whole, the identification of P¹, M³ and P₂ is believed to be reliable, while it is difficult to distinguish P₃ from P₄, M₁ from M₂ etc. Concerning the variations of the teeth, P¹ is the most variable one in dimension. In the Quaternary tapirs in China, some dental characters can be used as reliable indicators to evaluate their evolutionary levels. The degree of the atrophy of the upper canine relative to the caniniform I³ is reflected in the C/I³ diameter ratio, which is decreasing during evolution. P¹ changes considerably in outline and strength of the hypocone. Some forms are without hypocone, such as Tapirus sanyuanensis, some have a very faint hypocone, such as Tapirus indicus; although most of them show a developed hypocone. For other cheek teeth, the W/L ratio is decreasing through geologic time. Two lineages can be tentatively proposed: one is the Tapirus peii-Tapirus sinensis-Megatapirus augustus progression; the other is the T. sanyuanensis-T. indicus lineage. T. sanyuanensis and T. peii stand on the base, and it is very probable that the latter is more primitive.