title: Khoratpithecus piriyai, a Late Miocene hominoid of Thailand.
abstract: A Khoratpithecus piriyai lower jaw corresponds to a well-preserved Late Miocene hominoid fossil from northeastern Thailand. Its morphology and internal structure, using a microcomputed tomography scan, are described and compared to those of other known Miocene hominoids. It originated from fluviatile sand and gravel deposits of a large river, and was associated with many fossil tree trunks, wood fragments, and large vertebrate remains. A biochronological analysis by using associated mammal fauna gives an estimated geological age between 9-6 Ma. The flora indicates the occurrence of a riverine tropical forest and wide areas of grassland. K. piriyai displays many original characters, such as the great breadth of its anterior dentition, suggesting large incisors, large lower M3, a canine with a flat lingual wall, and symphysis structure. Several of its morphological derived characters are shared with the orangutan, indicating sister-group relationship with that extant ape. This relationship is additionally strongly supported by the absence of anterior digastric muscle scars. These shared derived characters are not present in Sivapithecus, Ankarapithecus, and Lufengpithecus, which are therefore considered more distant relatives to the orangutan than Khoratpithecus. The Middle Miocene K. chiangmuanensis is older, displays more primitive dental characters, and shares several dental characters with the Late Miocene form. It is therefore interpreted as its probable ancestor. But its less enlarged M3 and more wrinkled enamel may suggest an even closer phylogenetic position to orangutan ancestors, which cannot yet be supported because of the incomplete fossil record. Thus Khoratpithecus represents a new lineage of Southeast Asian hominoids, closely related to extant great ape ancestors.
authors.affiliation: Paleontological Section, Department of Mineral Resources, Bureau of Geological Survey, Bangkok 10400, Thailand.
authors.forename: Yaowalak
authors.initials: Y
authors.lastname: Chaimanee
authors.forename: Chotima
authors.initials: C
authors.lastname: Yamee
authors.forename: Pannipa
authors.initials: P
authors.lastname: Tian
authors.forename: Kitti
authors.initials: K
authors.lastname: Khaowiset
authors.forename: Bernard
authors.initials: B
authors.lastname: Marandat
authors.forename: Paul
authors.initials: P
authors.lastname: Tafforeau
authors.forename: Christian
authors.initials: C
authors.lastname: Nemoz
authors.forename: Jean-Jacques
authors.initials: JJ
authors.lastname: Jaeger
mesh_terms: D000818:Animals; D000885:Anthropology, Physical; D005075:Biological Evolution; D019229:Dentition, Permanent; D004777:Environment; D005580:Fossils; D015186:Hominidae / Q000033:anatomy & histology*; D007091:Image Processing, Computer-Assisted; D008334:Mandible / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D011859:Radiography; D013785:Thailand; D014070:Tooth / Q000033:anatomy & histology* / Q000000981:diagnostic imaging