Original paper
New materials of Khoratpithecus, a late Miocene hominoid from Nakhon Ratchasima Province, Northeastern Thailand, confirm its pongine affinities
Chaimanee, Yaowalak; Lazzari, Vincent; Yamee, Chotima; Suraprasit, Kantapon; Rugbumrung, Mana; Chaivanich, Kamol; Jaeger, Jean-Jacques
Palaeontographica Abteilung A Band 323 Lieferung 4-6 (2022), p. 147 - 186
68 references
published: Sep 1, 2022
published online: Aug 4, 2022
manuscript accepted: Mar 26, 2022
manuscript received: Sep 18, 2021
Abstract
Khoratpithecus piriyai is a large-bodied hominoid documented from the late Miocene locality of Khorat sand pit in Nakhon Ratchasima province, northeastern Thailand that was previously known anatomically from a mandible fragment and a partial maxilla. Here we describe additional four mandible fragments and one hemi-maxilla, all of which originating from the same sedimentary unit. Most of these new specimens are assigned to K. piriyai based on their dentognathic morphology. However, one larger specimen forms the basis for the new species, Khoratpithecus magnus n. sp. These specimens provide important new information about Khoratpithecus and help to understand the morphological variability of this taxon, enabling us to propose an emended diagnosis for the genus. The absence of scars for the anterior digastric muscles, a uniquely derived character only shared with Pongo, characterizes all new lower jaws that preserved the base of the symphysis and constitutes a significant character for this genus, together with the strong robustness of the mandibular corpora. Some characters show high variation, such as the intercanine breadth of the lower jaws which, when reduced, induces a divergent shape of the tooth rows, a feature that also occurs in the closely related taxa, Ankarapithecus and Sivapithecus. This character is present in all new specimens referred to K. piriyai. The new species, K. magnus, displays many similarities with Khoratpithecus piriyai, but differs from it by its larger size, having a body mass estimated as 30 % larger than that of K. piriyai, combined with several distinct dental characters, including higher crown height and length/width molar proportions. Its lower jaw displays canine alveolar sizes similar to those of the other individuals from the same locality, which are of smaller size. Therefore, these differences cannot be attributed to sexual dimorphism, justifying the erection of a new species. These specimens also shed new light on the feeding adaptation of this genus. Several characters, including the rather small P3, reduced honing facets,thick enamel, large molar crowns, very robust mandibular corpora, high crowned molars and a tendency for heavy wear on the cheek teeth, point to a dental adaptation for an abrasive diet similar to that of Indopithecus. However, the comparison between these two genera suggests that their similarities are the result of an adaptation to an abrasive diet, reflecting homoplasy within the pongid clade. The climatic and vegetational changes occurring in South Asia during the late Miocene probably instigated these adaptative changes among three different large-bodied hominoids, Khoratpithecus Indopithecus and the unknown ancestor of Gigantopithecus.
Keywords
Southeast Asia • Thailand • Miocene • orangutan • ape