Bos gaurus (Hamilton-Smith, 1827)

Suraprasit, Kantapon, Jaeger, Jean-Jacques, Chaimanee, Yaowalak, Chavasseau, Olivier, Yamee, Chotima, Tian, Pannipa & Panha, Somsak, 2016, The Middle Pleistocene vertebrate fauna from Khok Sung (Nakhon Ratchasima, Thailand): biochronological and paleobiogeographical implications, ZooKeys 613, pp. 1-157 : 43-45

Taxon classification Animalia Artiodactyla Bovidae

Bos gaurus (Hamilton-Smith, 1827)

Referred material.

A left horn core, DMR-KS-05-03-26-22; a right DP2, DMR-KS-05-03-20-4; two right P2-DMR-KS-05-03-19-27 and DMR-KS-05-04-03-3; a right DP3, DMR-KS-05-03-20-3; a right DP4, DMR-KS-05-03-17-3; a right M1, DMR-KS-05-03-00-20; a right M3, DMR-KS-05-03-17-1; a right mandible with m1-m3, DMR-KS-05-03-00-1; a left mandible with p2-m3, DMR-KS-05-04-3-1; a left i1, DMR-KS-05-03-00-27; two left m2-DMR-KS-05-03-19-26 and DMR-KS-05-03-16-1; two humeri-DMR-KS-05-05-1-1 (right) and DMR-KS-05-03-00-62 (left); a right metacarpus, DMR-KS-05-03-26-27; two left femora-DMR-KS-05-03-9-2 and DMR-KS-05-04-30-1 (proximal part).

Material description.

Horn core: a single horn core (DMR-KS-05-03-26-22) is small, curved upward (Fig. 28A, B) and slightly backward. The horn core base is oval in cross-section (Fig. 28A). A longitudinal ridge on the anterior surface of the horn core is present (Fig. 28B). This specimen belongs to a juvenile individual according to its very small size.

Upper dentition: DP2 (DMR-KS-05-03-20-4) is small and elongated, characterized by three main cones (anterior cone, paracone, and metacone) and a well-developed metastyle (Fig. 28C) (for measurements, see Tab. 15). The anterior and poste rior fossettes fuse together. Two P2 (DMR-KS-05-03-19-27; Fig. 28D and DMR-KS-05-04-03-3: Fig. 28E) have a well developed paracone rib close to the parastyle and a nearly flat lingual wall. The fossettes are separated into two islands (larger for the anterior one) due to the heavy wear stage (Fig. 28D). The P2 shows a nearly straight posterior wall and is wider than the DP2 (Fig. 28E). On the molarized DP3, the posterior lobe is broader than the anterior lobe (Fig. 28F). A small medial fossette is present. The entostyle is short and projects posteriorly. The molarized DP4 (DMR-KS-05-03-17-3) is slightly worn, characterized by a rectangular outline, well-developed buccal styles, an unfused entostyle, and two separated medial fossette (Fig. 28 G–H). The entostyle is bifurcated and situated between the protocone and hypocone (Fig. 28G). Two parallel longitudinal grooves are present along the lingual surface of the enstostyle, likely resulting in a trifurcated pattern in relation to the middle wear stage (Fig. 28H). The heavily worn M1 (DMR-KS-05-03-00-20) displays a subsquare outline and an unbifurcated entostyle positioned between the protocone and hypocone (Fig. 28I). The medial fossette is absent due to the heavy wear stage. The M3 (DMR-KS-05-03-17-1) exhibits well-developed buccal styles and large medial fossettes splitting into 2 islands with wear (Fig. 28J). The entostyle on the M3 is short, not bifurcated, and close to the hypocone.

Mandibles and lower dentition: DMR-KS-05-04-3-1 is complete, posterior to the p2, with the exception of a small part of the angular region (Fig. 28K, L) (for measurements, see Appendix 13). Another mandible (DMR-KS-05-03-00-1) preserves only a portion of the ramus with the complete molar row (Fig. 28M and Appendix 13). The isolated i1 (DMR-KS-05-03-00-27) is heavily worn, spatulate, and robust. Lower premolars have well-developed main cuspids and cristids (Fig. 28K, M). On the p2, the protocone is the highest cuspid and the posterior fossette is present. The p3 is elongated as long as the p4. The premetacristid is poorly developed. The postprotocristid on the p3 is larger than that on the p4. On the p4, the postprotocristid is narrow and anteroposteriorly constricted. The metaconid is most developed, compared to Bos sauveli and Bos javanicus as well as Bubalus arnee . For all lower molars, the ectostylid is slightly developed and not bifurcated (Fig. 28K, M–N) (for measurements, see Tab. 15). In lingual view, the metastylid is absent at the medium wear stage (Fig. 28K, M). In occlusal view, the entostylid is straight and short. The buccal outline of the protoconid and hypoconid is U-shaped in relation to the strong wear (Fig. 28M). The posterior talonid on the m3 is well-developed. The posthypoconulidcristid protrudes posteriorly.

Postcranial remains: postcranial elements include humeri (Fig. 29 A–D), a metacarpus (Fig. 29 E–G), and femora (Fig. 29 H–J) (for measurements, see Appendix 1). The femur DMR-KS-05-04-30-1 lacks a distal portion. We assign these postcranial bones based on the proportional correlations with the recent specimens of Bos gaurus (Tab. 13 and Appendices 7 and 9-12).

Taxonomic remarks and comparisons.

According to IUCN (2015), the wild forms of gaurs are considered as Bos gaurus , while their domestic forms are recognized as Bos frontalis ( Gentry et al. 2004). We consider here the Pleistocene fossil gaurs as belonging to wild forms in terms of taxonomic nomenclature.

We assign the juvenile horn core (DMR-KS-05-03-26-22) to Bos gaurus because the horn cores of gaurs are different from all other Bos species. They grow outward and curve upward, similar to those of Bubalus arnee , but their apical portion curves inward and slightly forward ( Lekagul and McNeely 1988).

Mandibles and isolated teeth of Bos gaurus are also observed. The cheek teeth of Bos gaurus are distinguished from Bos sauveli and Bos javanicus by having two separate fossettes on the P2, more developed metaconids and more anteroposteriorly constricted postprotocristids on the p3 and p4, and more robust cheek teeth (Figs 26 and 27, and Tab. 15). The entostyles are usually bifurcated or sometimes trifurcated on the slightly to moderately worn upper molars (our observations on the comparative material of recent Bos gaurus : e.g., ZSM-1972-5 and ZSM-1961-313), similar to those of Bos javanicus . But the entostyle is not bifurcated, when the molar is extremely worn, as seen on the specimen DMR-KS-05-03-00-20 (Fig. 28I). This character is therefore morphologically variable through wear. On the m3, the entostylid and posterior talonid in Bos gaurus is almost more developed than that in Bos javanicus . The angle between the posthypocristid and prehypoconulidcristid is slightly more divergent in Bos sauveli than in Bos gaurus . The size of Khok Sung Bos gaurus falls within the range of the recent population (Figs 26 and 27, and Tab. 14). We elucidate here the co-occurrence of two Bos species, Bos sauveli and Bos gaurus (larger), in Khok Sung.