Two isolated upper molars M1 of the ancient sun bear Helarctos malayanus praemalayanus (von Koenigswald, 1935) are described from the Middle Pleistocene deposits of the Tham Hai cave locality in northeastern Vietnam (Lang Son Province). Their structure shows morphological features typical for M1 of Middle Pleistocene representatives of the species. This is the first description of remains of H. m. praemalayanus from the Middle Pleistocene of Vietnam that expands understanding of the dental morphology and distribution of sun bears during the Pleistocene. Judging by dental measurements of H. malayanus from various localities of Southeast Asia, sun bears in the Middle Pleistocene were distinctly larger than modern ones. Apparently, at the end of the Late Pleistocene, sun bears became smaller and predominantly arboreal.
Lopatin et al. (Sun,) studied this question.