First Hominoid from the Late Miocene of the Irrawaddy Formation (Myanmar)

Jean-Jacques Jaeger,Soe Thura Tun,Kyaw Linn Oo,Aung Aung Khyaw,Pauline Coster,Franck Guy,Paul Tafforeau,Yaowalak Chaimanee,Olivier Chavasseau,Hervé Bocherens,Kamol Chaivanich,Hla Shwe,Mouloud Benammi,Aung Naing Soe,Aye Maung,Renaud Lebrun,Mana Rugbumrung,Edouard-Georges Emonet

doi:10.1371/journal.pone.0017065

Abstract

For over a century, a Neogene fossil mammal fauna has been known in the Irrawaddy Formation in central Myanmar. Unfortunately, the lack of accurately located fossiliferous sites and the absence of hominoid fossils have impeded paleontological studies. Here we describe the first hominoid found in Myanmar together with a Hipparion (s.l.) associated mammal fauna from Irrawaddy Formation deposits dated between 10.4 and 8.8 Ma by biochronology and magnetostratigraphy. This hominoid documents a new species of Khoratpithecus, increasing thereby the Miocene diversity of southern Asian hominoids. The composition of the associated fauna as well as stable isotope data on Hipparion (s.l.) indicate that it inhabited an evergreen forest in a C3-plant environment. Our results enlighten that late Miocene hominoids were more regionally diversified than other large mammals, pointing towards regionally-bounded evolution of the representatives of this group in Southeast Asia. The Irrawaddy Formation, with its extensive outcrops and long temporal range, has a great potential for improving our knowledge of hominoid evolution in Asia.

Highlights

Paleontological research in the Irrawaddy Formation and recent findingsDespite more than a century of intense research on the issue, the origin of the Pleistocene to extant orang-utan Pongo is poorly understood
The long temporal range and extensive outcrops of the Irrawaddy Formation in Central Myanmar, where sediments range from the middle Miocene to the Pleistocene [5,6], offer unique opportunities to complete the Asian hominoid fossil record
The genus Khoratpithecus is known from two others localities in Thailand; with Khoratpithecus chiangmuanensis in Chiang Muan basin in Northern Thailand [3] and Khoratpithecus piriyai in Nakorn Ratchasima Province, in Northeastern Thailand [4,18]

Summary

Introduction

Paleontological research in the Irrawaddy Formation and recent findingsDespite more than a century of intense research on the issue, the origin of the Pleistocene to extant orang-utan Pongo is poorly understood. The Irrawaddy Formation has yielded numerous terrestrial mammal remains since the 19th century [7,8,9,10,11,12] Despite these numerous reports, only a few precisely located fossiliferous sites have been described from this Formation [13], affecting the reliability of most of paleontological studies. This situation is well illustrated by the Yenangyaung region, type area of the Irrawaddy Formation, whose fossils were interpreted as belonging either to a single fauna [14] or to two faunas [10,15,16], and variously dated [6]

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Results

Conclusion