The Middle Pleistocene vertebrate fauna from Khok Sung (Nakhon Ratchasima, Thailand): biochronological and paleobiogeographical implications

Abstract

The fluviatile terrace deposits of Khok Sung, Nakhon Ratchasima province, have yielded more than one thousand fossils, making this the richest Pleistocene vertebrate fauna of Thailand. The excellent preservation of the specimens allows precise characterization of the faunal composition. The mammalian fauna consists of fifteen species in thirteen genera, including a primate, a canid, a hyaenid, proboscideans, rhinoceroses, a suid, cervids, and bovids. Most species correspond to living taxa but globally (Stegodon cf. orientalis) and locally (Crocuta crocuta ultima, Rhinoceros unicornis, Sus barbatus, and Axis axis) extinct taxa were also present. The identification of Axis axis in Khok Sung, a chital currently restricted to the Indian Subcontinent, represents the first record of the species in Southeast Asia. Three reptilian taxa: Crocodylus cf. siamensis, Python sp., and Varanus sp., are also identified. Faunal correlations with other Southeast Asian sites suggest a late Middle to early Late Pleistocene age for the Khok Sung assemblage. However, the Khok Sung mammalian fauna is most similar to that of Thum Wiman Nakin, dated to older than 169 ka. The Khok Sung large mammal assemblage mostly comprises mainland Southeast Asian taxa that migrated to Java during the latest Middle Pleistocene, supporting the hypothesis that Thailand was a biogeographic pathway for the Sino-Malayan migration event from South China to Java.

Direct ESR dating of the Pleistocene vertebrate assemblage from Khok Sung locality, Nakhon Ratchasima Province, Northeast Thailand

“…The Khok Sung assemblage includes diverse groups of large vertebrates, as well as some invertebrate remains such as gastropod shells. The reptilian assemblage comprises testudines, a gharial, a crocodile and squamates, while fish remains were tentatively attributed to large silurids (Claude et al, 2011;Martin et al, 2012;Suraprasit et al, 2016). One vertebral fragment of an unidentified bird, but belonging to the order Galliformes, was also found (Suraprasit et al, 2016).…”

“…The reptilian assemblage comprises testudines, a gharial, a crocodile and squamates, while fish remains were tentatively attributed to large silurids (Claude et al, 2011;Martin et al, 2012;Suraprasit et al, 2016). One vertebral fragment of an unidentified bird, but belonging to the order Galliformes, was also found (Suraprasit et al, 2016). The mammalian assemblage contains 15 species from 13 genera including extinct and extant large-sized taxa: a primate, carnivores, proboscideans, rhinoceroses, a suid, cervids and bovids (see Table 1 for the complete faunal list) (Suraprasit et al, 2016).…”

“…One vertebral fragment of an unidentified bird, but belonging to the order Galliformes, was also found (Suraprasit et al, 2016). The mammalian assemblage contains 15 species from 13 genera including extinct and extant large-sized taxa: a primate, carnivores, proboscideans, rhinoceroses, a suid, cervids and bovids (see Table 1 for the complete faunal list) (Suraprasit et al, 2016).…”

“…Additionally, located at the interface between mainland Southeast Asia and Indonesian islands, Thailand holds a key position for the understanding of large mammal and human dispersals between these two distinct biogeographical areas (also named as Indochina and Sunda provinces) during the Pleistocene. Consequently, the study of the Thai palaeontological record is crucial for reconstructing migration pathways (e.g., Siva-Malayan and Sino-Malayan routes) and testing the relevance of different hypotheses (e.g., the savannah corridor) regarding the environmental conditions favouring these dispersals (e.g., Bird et al, 2005;Louys and Meijaard, 2010;Suraprasit et al, 2016;Tougard, 2001). In particular, the savannah corridor hypothesis has been proposed to explain the dispersal from China to Sundaic subregion of several open grassland species, and especially that of Homo erectus, during the glacial periods of the Pleistocene.…”

“…In particular, the savannah corridor hypothesis has been proposed to explain the dispersal from China to Sundaic subregion of several open grassland species, and especially that of Homo erectus, during the glacial periods of the Pleistocene. However, the large mammal Pleis-tocene record of Thailand remains overall poorly documented compared with that of other Southeast Asian countries, due to a combination of inappropriate taxonomic identifications, a lack of numerical dating studies and the limited number of fossil sites currently available (Suraprasit et al 2016;Louys and Meijaard, 2010). This is why numerical dating results are urgently required to overcome at least one of these issues.…”