New hominoid mandible from the early Late Miocene Irrawaddy Formation in Tebingan area, central Myanmar

抄録

A new medium-sized hominoid mandibular fossil was discovered at an early Late Miocene site, Tebingan area, south of Magway city, central Myanmar. The specimen is a left adult mandibular corpus preserving strongly worn M₂ and M₃, fragmentary roots of P₄ and M₁, alveoli of canine and P₃, and the lower half of the mandibular symphysis. In Southeast Asia, two Late Miocene medium-sized hominoids have been discovered so far: Lufengpithecus from the Yunnan Province, southern China, and Khoratpithecus from northern Thailand and central Myanmar. In particular, the mandibular specimen of Khoratpithecus was discovered from the neighboring village of Tebingan. However, the new mandible shows apparent differences from both genera in the shape of the outline of the mandibular symphyseal section. The new Tebingan mandible has a well-developed superior transverse torus, a deep intertoral sulcus (= genioglossal fossa), and a thin, shelf-like inferior transverse torus. In contrast, Lufengpithecus and Khoratpithecus each have very shallow intertoral sulcus and a thick, rounded inferior transverse torus. The characteristic morphology of the mandibular symphysis in the Tebingan specimen suggests a different taxon from Khoratpithecus. In central Myanmar at least two kinds of medium-sized hominoids were likely present in the early Late Miocene.