Rusa unicolor (Kerr, 1792)

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 : 36-40

Taxon classification Animalia Artiodactyla Cervidae

Rusa unicolor (Kerr, 1792)

Referred material.

Three right antlers-DMR-KS-05-03-20-11 (nearly complete specimen), DMR-KS-05-03-26-2 (fragment), and DMR-KS-05-03-28-23 (fragment); a right M1, DMR-KS-05-03-22-10; two left M2-DMR-KS-05-04-9-3 and DMR-KS-05-04-3-3; a left M3, DMR-KS-05-03-31-1; two right mandibles-DMR-KS-05-03-31-2 (with m2) and DMR-KS-05-03-13 (with p4-m3); two left mandibles-DMR-KS-05-03-00-101 (with p3-m3) and DMR-KS-05-03-27-4 (with m3); a right m1, DMR-KS-05-03-00-5; a left fragmentary humerus, DMR-KS-05-03-15-43 (distal part); three right fragmentary radii-DMR-KS-05-03-25-9 (proximal part), DMR-KS-05-03-19-14 (proximal part), and DMR-KS-05-03-26-19 (distal part); a left metacarpus, DMR-KS-05-03-17-26; six fragmentary femora-DMR-KS-05-03-19-7 (right proximal part), DMR-KS-05-03-12-2 (right proximal part), DMR-KS-05-04-11-2 (right distal part), DMR-KS-05-03-26-5 (left proximal part), DMR-KS-05-04-30-9 (left distal part), and DMR-KS-05-04-19-10 (left distal part); a right tibia, DMR-KS-05-03-28-16; a right metatarsus, DMR-KS-05-03-19-11

Material description.

Antlers: DMR-KS-05-03-20-11 is a nearly complete antler, slightly broken at the middle part of the main beam (Fig. 23A). The fragmentary antler DMR-KS-05-03-26-2 comprises a burr, a broken brow tine, and a half of the main beam (Fig. 23B). The specimen DMR-KS-05-03-28-23 preserves the broken brow tine and main beam (Fig. 23C). The antler surface is rough. The shed antlers are morphologically characterized by three main tines, a long and slender main beam, a forked construction at the tip, and a well-developed burr (Fig. 23 A–C). On the apical bifurcation, the postero-internal tine is much shorter than the antero-external one. The main beam and brow tine are also much more robust, compared to the extant males of Axis porcinus (e.g., the specimen MNHN-ZMO-1904-60 and NMW-2546). The divergent angle between the main beam and brow tine ranges from 50° to 90°. The shed antlers of Rusa unicolor are different from those of Axis axis in having slightly rougher surfaces, more divergent insertion relative to the frontal orientation, a shorter main beam, and a smaller angle between the main beam and the brow tine, and in lacking small-ornamented tines or knobs on the brow tine (Fig. 23 A–C). These characters match well the recent Rusa unicolor .

Upper dentition: upper molars are robust (Tab. 12) and show well-developed styles (particularly the mesostyle), anterior cingula, and entostyles (Fig. 23D, E). The entostyle is bifurcated, like in Panolia eldii , in relation to the moderately to strongly worn teeth. The fossettes are present at least in the middle stage of wear. The metaconule fold is poorly developed or sometimes absent. On the M3, the anterior lobe is wider than the posterior one (Fig. 23E).

Mandibles and lower dentition: four mandibles are incomplete (for measurements, see Appendix 5). The specimens DMR-KS-05-03-13 (Fig. 23F, G) and DMR-KS-05-03-00-101 (Fig. 23H, I) preserve a partially broken mandibular body. The manidibles DMR-KS-05-03-31-2 and DMR-KS-05-03-27-4 are very fragmentary. All lower cheek teeth of Rusa unicolor are obviously larger than those of other Khok Sung cervids (Tab. 12). Lower molars display cervid-like patterns, such as well developed styles, anterior cingulids, and ectostylids (Fig. 23J, K). On the m3, the posterior lobe of the talonid in Rusa unicolor is more developed than those in Axis . Moreover, the posterior ectostylid is present (Fig. 23G, I, K), unlike in Axis .

Postcranial remains: postcranial elements include a humerus (Fig. 24 A–C), radii (Fig. 24 D–G), a metacarpus (Fig. 24 H–J), femora (Fig. 24 K–N), a tibia (Fig. 24 O–Q), and a metatarsus (Fig. 24 R–T). All radii and femora are fragmentary. We assign these postcranial bones to Rusa unicolor according to the sized and proportional correlation with the extant specimens (Tab. 13 and Appendices 1 and 7-12).

Taxonomic remarks and comparisons.

According to Leslie (2011), we regard here Rusa as a separate genus within the family Cervidae . Four species are currently recognized: Rusa unicolor (sambar), Rusa marianna (Philippine deer), Rusa timorensis (rusa), and Rusa alfredi (Prince Alfred’s deer).

Antlers of Rusa unicolor are characterized by its typical three tines and forked beams at the tip, similar in shape to those of Axis porcinus but much more robust. The sambar deer shares a similar dental morphology with the Eld’s deer. But it differs from Panolia eldii as well as Axis axis in being larger-sized and in having more developed anterior cingulids on lower molars. The sambar deer is much larger than Axis axis (Figs 21 and 22). Based on the body mass estimated from the second molar sizes, Khok Sung large cervids fit well the size tendency of the modern populations of Rusa unicolor (Tab. 14). As demonstrated by the scatter diagrams (Figs 21 and 22), the recent sambar deer shows a wide range of size variation that sometimes overlaps with the Eld’s deer. The cheek teeth of Khok Sung Rusa unicolor conform to the size variability of their recent population. They are also comparable in size and morphology to the fossil sambar deer from Thum Prakai Phet ( Filoux et al. 2015), Phnom Loang ( Beden and Guérin 1973), and Ma U’Oi ( Bacon et al. 2004) (Figs 21 and 22). As is the case for Panolia eldii , some cervid specimens described from Thum Wiman Nakin are improperly identified. For instance, the P2 (TF 3371 and TF 4570) probably do not belong to Rusa unicolor according to their smaller sizes. The taxonomic revision of fossil cervids from Thum Wiman Nakin would lead to the recognition of either higher or lower diversity of cervids in Southeast Asia during the Middle Pleistocene.