Additional materials of Myanmarpithecus yarshensis (Amphipithecidae, Primates) from the middle Eocene Pondaung Formation.

Myanmarpithecus yarshensis is an amphipithecid primate from the middle Eocene Pondaung Formation in Myanmar. It was previously known based on maxillary fragments with P(4)-M(3) and mandibular fragments with C-P(3) and M(2-3). This study reports new materials for the genus, including a humeral head fragment, a lingual fragment of the right M(2), a lingual fragment of the right M(3), and a left I(1). These new materials were collected from approximately the same point, and likely belonged to the same individual. The upper molar morphology and size of the new materials show similarity to those of the type specimen, indicating that the new materials can be assigned to M. yarshensis. The humeral head is the first postcranial element that is associated with dental materials for amphipithecids. The morphological similarity between the previously reported larger humerus and this specimen confirms the assignment of the former specimen to Amphipithecidae and suggests common locomotor adaptations in the family. The upper central incisor is large relative to the molar fragments, but is within the variation among extant platyrrhines. The tooth is spatulate-shaped and high crowned, and lacks the mesial process, indicating similarity to I(1) of haplorhines and clear differences from that of adapoids. It has been suggested that amphipithecids, including Myanmarpithecus, have affinities with notharctine adapoids, but the morphology of I(1) does not support the notharctine hypothesis of the Amphipithecidae.