The Middle Pleistocene vertebrate fauna from Khok Sung (Nakhon Ratchasima, Thailand): biochronological and paleobiogeographical implications Author Suraprasit, Kantapon Author Jaeger, Jean-Jacques Author Chaimanee, Yaowalak Author Chavasseau, Olivier Author Yamee, Chotima Author Tian, Pannipa Author Panha, Somsak text ZooKeys 2016 613 1 157 http://dx.doi.org/10.3897/zookeys.613.8309 journal article http://dx.doi.org/10.3897/zookeys.613.8309 1313-2970-613-1 0FDE9BAB3DD4402DB6E1177639C32D43 0FDE9BAB3DD4402DB6E1177639C32D43 Taxon classification Animalia Primates Cercopithecidae Macaca sp. Referred material. A right tibia, DMR-KS-05-04-04-1. Material description. The right tibia is complete (Fig. 6 A-D ) and elongated (for measurements, see Appendix 1). On the proximal articular surface, the medial condyle is as large as the lateral one. The lateral condyle is convex anteroposteriorly (Fig. 6C). The posteromedial margin of the lateral condyle lacks a notch that indicates a single meniscus attachment. At the proximal end, the tibial tuberosity is developed. The shaft is elongated, anteriorly and laterally bowed, and not anteroposteriorly compressed (Fig. 6A, B). Distally, the trochlear surface is trapezoid in outline (Fig. 6D). The medial malleolus is well-developed and projects more anteriorly than posteriorly. The medial and lateral parts of the trochlear surface are equally separated by a weak median keel. Figure 6. Postcranial remains of Macaca sp. A-D and Cuon sp. E-H from Khok Sung: A-D DMR-KS-05-04-04-1, a right tibia in anterior (A), medial (B), proximal (C), and distal (D) views E-F DMR-KS-05-04-11-34, a right ulna in medial (E) and anterior (F) views G-H DMR-KS-05-04-28-13, a right femur in proximal (G) and posterior (H) views. Taxonomic remarks and comparisons. Tibial morphology is relatively conservative within and among primates. Particularly, the morphological differences of tibiae among cercopithecoids are minimal ( Turley et al. 2011 ). The distal part of tibiae of arboreal primates (including Hylobates and all arboreal cercopithecoids) is characterized by more rounded borders of the trochlear surface and a convex proximal border of the medial malleolus joining the trochlear surface ( Tallman et al. 2013 ). The specimen DMR-KS-05-04-04-1 shows typical characters of the recent cercopithecoids whose tibial shaft is less mediolaterally compressed than those of great apes. However, the tibia from Khok Sung represents compatible dimensions with the tibiae of Hylobates (gibbon), Presbytis (surili), and Macaca (macaque). We suggest here to make a distinction between these genera based on the ratios of the greatest length of the tibia to the length or width of the proximal tibia (GL/Bp or GL/Dp). Based on these indices, the Khok Sung tibia falls within the range of recent Macaca (Tab. 2). According to the ratios , the shaft of both the surilis and gibbons is more elongated, compared to that of macaques. The distal tibia of DMR-KS-05-04-04-1 also shares some additional characters with that of macaques such as the poorly developed ball-shaped convexity and -articular facet ( Sondaar et al. 2006 ) and the shape of the trochlear surface ( Tallman et al. 2013 : Fig. 5). We therefore attribute this material to Macaca sp. Table 2. Ratios of the greatest lengths of tibiae (GL) to the lengths and widths of proximal and distal tibiae (Bp, Dp, Bd, and Dd) of Khok Sung macaques compared to recent Southeast Asian primates.

DMR-KS-05-04-04-1	Presbytis (N = 30)			Hylobates (N = 24)			Macaca (N = 71)
	Max	Min	Mean	Max	Min	Mean	Max	Min	Mean
GL/Bp
GL/Dp
GL/Bd
GL/Dd