Wednesday, August 31, 2016

[Paleontology • 2016] The Middle Pleistocene Vertebrate Fauna from Khok Sung (Nakhon Ratchasima, Thailand): Biochronological and Paleobiogeographical Implications

Cranial remains of Axis axis from Khok Sung 

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.

Keywords: Large mammals, taxonomy, AiluropodaStegodon assemblage, paleobiogeography, late Middle Pleistocene, Quaternary, northeastern Thailand, mainland Southeast Asia

Figure 1. Map of Southeast Asia showing A the Sundaland boundaries and the migration route hypothesis: Siva-Malayan route (black), Sino-Malayan route (red), and Taiwan-Philippine Archipelago route (blue) and B the location of the Khok Sung sand pit (star) and other Middle (red circle) and Late (yellow circle) Pleistocene sites. The Sunda shelf boundaries at the sea level about 120 m lower than the present day are compiled from Voris (2000). Some Middle Pleistocene sites in South China and central Eastern China are shown in the map. Only Gua Cha (Peninsular Malaysia) is Holocene in age (Groves 1985, Bulbeck 2003).

Figure 2. Locality of Khok Sung:
A the sand pit during the paleontological excavation B the location of vertebrate fossils C the lithostratigraphic and paleomagnetic sections (modified from Suraprasit et al. 2015).

Figure 7. Dental remains of Stegodon cf. orientalis from Khok Sung:
A–B DMR-KS-05-03-28-14, a right DP4 in occlusal (A) and buccal (B) views C DMR-KS-05-03-19-7, an anterior lobe of DP4 in occlusal view D DMR-KS-05-04-01-8, a left dp3 in occlusal view E–F DMR-KS-05-03-29-1, a left posterior fragment of M2 in occlusal (E) and buccal (F) views G–H DMR-KS-05-03-22-19, a right posterior fragment of M3 in occlusal (G) and buccal (H) views I–K DMR-KS-05-03-15-2, a fragmentary upper tusk in proximal (I–J) and dorsal (K) views L DMR-KS-05-03-08-1, a left mandible with m3 in occlusal view M DMR-KS-05-03-08-2, a right mandible with m3 in occlusal view.

Figure 14. Cranial remains of Axis axis from Khok Sung:
 A–B DMR-KS-05-04-18-50, a cranium with nearly complete antlers in dorsal (A) and ventral (B) views C–D DMR-KS-05-03-00-30, a cranium in lateral (C) amd ventral (D) views E DMR-KS-05-03-18-X9, a cranium in anterior view F–G DMR-KS-05-03-27-1 a cranium in dorsal (F) and ventral (G) views H DMR-KS-05-03-31-30, a right antler in anterior view; (I) DMR-KS-05-03-22-4, a right antler in lateral view J DMR-KS-05-03-18-21, a left antler fragment in lateral view K DMR-05-03-22-2, a left antler fragment in lateral view L DMR-KS-05-03-19-81, a left antler fragment in medial view.

Figure 19. Remains of Panolia eldii from Khok Sung:
 A–C DMR-KS-05-04-20-4, a cranium in dorsal (A), lateral (B), and ventral (C) views D DMR-KS-05-03-15-11, a right P2 E DMR-KS-05-03-00-24, a left M1 F DMR-KS-05-03-00-23, a right M2 G DMR-KS-05-03-27-6, a left M3 H DMR-KS-05-04-9-2, a left M3 I DMR-KS-05-03-29-2, a right i1 in lingual view J–K DMR-KS-05-03-27-2, a left mandible in lateral (J) and occlusal (K) views L–M DMR-KS-05-04-9-5, a left mandible in occlusal (L) and lateral (M) views. All teeth are shown in occlusal view. 

Figure 30. Cranial and upper dental remains of Bubalus arnee from Khok Sung:
A–C DMR-KS-05-03-20-1, a cranium in dorsal (A), ventral (B), and lateral (C) views and D–E DMR-KS-05-03-21-1, a cranium in dorsal (D) and ventral (E) views F–G DMR-KS-05-03-11-1, a right upper jaw in lateral (F) and occlusal (G) views H–I DMR-KS-05-03-16-3, a partial cranium in ventral view (H) with a right tooth row (I) J DMR-KS-05-03-16-2, a right horn core in dorsal view K DMR-KS-05-03-18-14, a left P2 L DMR-KS-05-03-00-103, a left DP3 M DMR-KS-05-04-29-8, a right DP4 N DMR-KS-05-03-00-7, a right M3. Cross-sections of basal horn cores are given. All isolated teeth are shown in occlusal view. 

Kantapon Suraprasit, Jean-Jacques Jaeger, Yaowalak Chaimanee, Olivier Chavasseau, Chotima Yamee, Pannipa Tian and Somsak Panha. 2016. The Middle Pleistocene Vertebrate Fauna from Khok Sung (Nakhon Ratchasima, Thailand): Biochronological and Paleobiogeographical Implications.  ZooKeys. 613; 1-157. DOI: 10.3897/zookeys.613.8309

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