Late Pliocene Semnopithecus fossils from central Myanmar: rethinking of the evolutionary history of cercopithecid monkeys in Southeast Asia

Abstract

We here describe a new fossil species of Asian colobine monkey, Semnopithecus gwebinensissp. nov. from the Late Pliocene Irrawaddy sediments of the Gwebin area in central Myanmar. Extant Semnopithecus (Hanuman langur) is a relatively large, terrestrial colobine monkey known as one of the most adaptable non-human primates. It is widely distributed, mainly in the Indian subcontinent, from Pakistan in the west to Bangladesh in the east. However, in Myanmar Semnopithecus is not distributed but Trachypihtecus is, which is the closest relative to Semnopithecus. It is presumed that extant Trachypithecus pileatus, which is considered to be a hybrid of Semnopithecus and Trachypithecus from molecular biological studies, appeared in the Early Pleistocene as the result of hybridisation between the two genera. On the other hand, no fossil specimens of other cercopithecid monkeys, such as Macaca, Trachypithecus or Rhinopithecus, all of which are commonly discovered from the Pleistocene cave sediments of South China, have been found from the Pliocene sediments in central Myanmar to date. The dissimilarity in the primate fauna between central Myanmar and South China suggests little faunal interchange between the two regions probably because of geographical barriers such as large rivers and high mountain ranges in the area.

Keywords::

• Semnopithecus gwebinensis
• Late Pliocene
• Myanmar

Acknowledgements

We are grateful to Aung Naing Soe, Aung-Aung-Kyaw, Hla-Shwe, Myat-Swe, Kyaw Myo Win, Kyaw Soe Win and Zin Oo of the Department of Archaeology, Ministry of Culture, Myanmar, for their help in our palaeontological studies in Myanmar, and also to all research members who participated in the fieldworks in Myanmar. We thank E. Delson (AMNH); M. Pickford, B. Senut, P. Tassy, and C. Sagne (MNHN); Changzhu Jin and Yingqi Zhang (IVPP); Baoguo Li and Xiaoguang Qi (Northwest University, Xi'an, China); D. Shimizu and Y. Shintaku (Japan Monkey Centre, Inuyama); J. de Vos and R. van Zelst (National Natuurhistorisch Museum, Leiden, The Netherlands); R. Kruszynski and P. Jenkins (BMNH); E.V. Maschenko (PIN); Lim Kok Peng Kelvin (National University of Singapore, Singapore); and C. Nahallage (University of Sri Jayewardenepura, Sri Lanka) for graciously providing access to the specimens examined at their respective institutions.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Financial support was provided by the Japan Society for the Promotion of Science (JSPS) with Grants-in-Aid for Scientific Research to M. Takai [grant number 16405018], [grant number 20405015], [grant number 26304019].