Systematics and paleobiology of the anthropoid primate Pondaungia from the late Middle Eocene of Myanmar

Several newly recovered specimens documenting the Eocene Myanmar (South East Asia) anthropoid taxa Pondaungia and Amphipithecus modify the classical understanding of the taxonomy of these two primates, which have in fact no substantial morphological differences. Using tooth wear stages and the elevation of the horizontal branch of the mandible below the foramen mentale, we show a continuous variation, here attributed to individual aging. In addition, a strong size dimorphism is demonstrated, which is attributed to sexual dimorphism. In this context, Amphipithecus mogaungensis holotype is interpreted as a male of Pondaungia cotteri, which is recognized as the only large-bodied anthropoid of the Pondaung Formation. Growth arrest lines (LAGs) have been observed in several sections of lower jaws attributed to that species. These LAGs are here interpreted as regular increments, which formed in response to seasonal variability in the environment. They likely correspond to annual cycles, and the minimum longevity of the individuals can thus be roughly estimated. Several features indicate that P. cotteri may have been adapted to hard food diet and to survive in a strong seasonal climate with annual food shortage periods.