Axis axis (Erxleben, 1777)

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 : 26-31

Taxon classification Animalia Artiodactyla Cervidae

Axis axis (Erxleben, 1777)

Referred material.

Four crania-DMR-KS-05-04-18-50 (with two antlers), DMR-KS-05-03-00-30 (with left partial and right broken antlers), DMR-KS-05-03-18-X9 (with pedicles), and DMR-KS-05-03-27-1 (with pedicles); two right complete antlers-DMR-KS-05-03-31-30 and DMR-KS-05-03-22-4; a nearly complete left antler, DMR-KS-05-04-4-1; five right fragmentary antlers-DMR-KS-05-03-18-21, DMR-KS-05-03-19-82, DMR-KS-05-03-28-22, DMR-KS-05-06-22-2, and DMR-KS-05-03-28-1; eight left fragmentary antlers-DMR-KS-05-03-00-12, DMR-KS-05-03-19-81, DMR-KS-05-03-22-2, DMR-KS-05-03-24-1, DMR-KS-05-04-09-1, DMR-KS-05-03-19-13, DMR-KS-05-03-26-21, and DMR-KS-05-03-08-17; two left fragmentary maxilla-DMR-KS-05-03-28-6 (with M1-M3) and DMR-KS-05-03-08-31 (with P3, P4, and M1 root); a right P4, DMR-KS-05-04-01-3; a left M1, DMR-KS-05-04-28-5; a left M2, DMR-KS-05-03-14-5; thirteen right mandibles-DMR-KS-05-03-14-2 (with m3), DMR-KS-05-03-20-1 (with p4-m3), DMR-KS-05-03-20-2 (with m2 and m3), DMR-KS-05-03-22-7 (with m2 and m3), DMR-KS-05-04-03-1 (with p2-m3), and DMR-KS-05-03-27-3 (with m2 and m3), DMR-KS-05-03-19-1 (with p2-m3), DMR-KS-05-03-22-8 (with m2 and m3), DMR-KS-05-04-01-1 (with p2-m3), DMR-KS-05-03-24-4 (with m2), DMR-KS-05-03-26-12 (with m2 and m3), DMR-KS-05-04-7-10 (with p3, m1, and m2), and DMR-KS-05-03-26-10 (with p2-m1); eight left mandibles-DMR-KS-05-03-18-22 (with p2), DMR-KS-05-03-22-6 (with m1-m3), DMR-KS-05-03-27-22 (with p3-m2 sockets and broken m3), DMR-KS-05-04-09-2 (with p3, p4, m1 and m2 sockets, and m3), DMR-KS-05-03-00-102 (with p4 and m1), DMR-KS-05-03-19-2 (with m1-m3), DMR-KS-05-03-23-1 (with p2 and p3 roots and p4-m3), and DMR-KS-05-03-29-1 (with p2-m3); a left m1, DMR-KS-05-04-28-6; three m2-DMR-KS-05-03-25-4 (right), DMR-KS-05-03-00-104 (left), and DMR-KS-05-03-22-11 (left); four left m3-DMR-KS-05-04-9-4, DMR-KS-05-03-22-9, DMR-KS-05-04-01-2, and DMR-KS-05-03-08-33; three right fragmentary humeri (distal part)-DMR-KS-05-03-13-4, DMR-KS-05-04-11-32, and DMR-KS-05-03-17-17; six metacarpi-DMR-KS-05-03-18-2 (right), DMR-KS-05-03-19-3 (right), DMR-KS-05-03-22-28 (right), DMR-KS-05-03-08-2 (right), DMR-KS-05-04-30-20 (right proximal fragment), and DMR-KS-05-03-19-37 (left); a right fragmentary femur, DMR-KS-05-03-27-4 (distal part); three metatarsi-DMR-KS-05-03-26-3 (right), DMR-KS-05-03-29-30 (left), and DMR-KS-05-03-15-14 (left).

Material description.

Crania and upper dentition: four crania are almost complete, lacking only the anterior portions (e.g., nasal, jugal, palatine, and maxilla) (Fig. 14 A–D). The specimen DMR-KS-05-04-18-50 shows nearly complete antlers, lacking only the left brow tine (Fig. 14A, B). The cranium DMR-KS-05-03-00-30 possesses a right antler portion preserving the complete brow tine but the broken main beam (Fig. 14C, D). The specimens DMR-KS-05-03-18-X9 (Fig. 14E) and DMR-KS-05-03-27-1 (Fig. 14F, G) preserve most of the rear part of the skull but lacks zygomatic arcs and antler portions. The specimen DMR-KS-05-03-27-1 preserves a deformed frontal area and broken pedicles (Fig. 14F). The basioccipital and basisphenoid are subtriangular in ventral view and show well-deveoped anterior and posterior tuberosities with a longitudinal groove running along the central part (Fig. 14B, D, G). The lateral edges of the basioccipital and basisphenoid are concave like in Axis . The foramina ovale are large and open ventrolaterally. The shed antlers are characterized by three main tines, smooth surfaces, a short pedicle and brow tine, a long and slender main beam, a high angle (about 100-120°) between the main beam and the brow tine, and a well-developed burr (Fig. 14A, C, H–L). A small ornamented tine (or knob) is sometimes present along the dorsal surface of the brow tine or at the main beam-brow tine junction (Fig. 14C, J–L). The main beam is oriented upward, laterally, and posteriorly, and consists of forked tines apically. At the antlered crown, the inner tine is much shorter than the outer one (Fig. 14A, H, I). The skull and antler exhibit a typical arrangement of recent Axis axis (e.g., the orientation of the main beam and brow tine, the bifurcation at the apical crown tine, and the shape of the basioccipital and basisphenoid) (for measurements, see Appendix 4).

P3 and P4 are similar to recent Axis , characterized by well-developed styles, medial cristae (more distinct on the P4), and posterolingual fossettes (Fig. 15A) (for measurements, see Tab. 12). On the P4, the medial cristae join the postmetacrista and divide the fossa into two islands (Fig. 15A, C). Upper molars display distinct styles (particularly the mesostyle), entostyles, and anterior cingula (Fig. 15B, D, E). The metaconule fold is slightly developed. The M2 is slightly wider than the M3 (Tab. 12). The posterior lobe of the M3 is reduced in width (Fig. 15B).

Mandibles and lower dentition: twenty one mandibles range from fragmentary (preserving only the broken corpus) to nearly complete (lacking only the ascending ramus and coronoid process) individuals (Fig. 15 F–O) (for measurements, see Appendix 5). The mandibular symphyses are almost complete, but all incisors are missing. The protoconulid of the p2 is poorly-developed or absent (Fig. 15F, H, J).

Lower third and fourth premolars exhibit a well developed metaconid which projects obliquely in occlusal view, posterior to the entoconid (Fig. 15F, H, J) (for measurements, see Tab. 12). The latter conid joins the posthypocristid, forming a back valley on moderately worn teeth. The metaconid is bifurcated (two separated flanges: pre- and postmetacristids) on the p4. All lower molars are morphologically characterized by their brachyodont crowns and well-developed stylids (parastylid, metastylid, and entostylid), ectostylids (basal pillars), and anterior cingulids (also called "goat fold") (Fig. 15 F–Q). On the m3, the posterior ectostylid is absent (Fig. 15F, G, J–Q). The third lobe is ring-shaped as it is present on the recent specimens (e.g., MNHN-ZMO-1901-547, MNHN-ZMO-1988-153, ZSM-1951-70, and ZSM-1961-3) (Fig. 15F, P). But the third lobe is sometimes small and poorly-developed, as observed from the recent specimen ZSM-1963-27 (Fig. 15J, L, N). The back fossa is present on unworn to slightly worn teeth (Fig. 15F, P), but absent on moderately to heavily worn ones (Fig. 15L, N). The posthypoconulidcristid is well-developed, a small crest protruding slightly more posterolingually (Fig. 15F).

Postcranial remains: postcranial bones include isolated humeri (Fig. 16 A–B), metacarpi (Fig. 16 C–H), a femur (Fig. 16I, J), and metatarsi (Fig. 16 K–M). The humerus and femur are fragmentary. We identify here these fossil postcranial bones based on the size and proportion compared with the extant specimens (Tab. 13 and Appendices 1, 7, 9-10, and 12).

Taxonomic remarks and comparisons.

The antlers are useful to distinguish among the cervids, whereas the morphologies of lower cheek teeth are identical among Axis . The skulls, antlers, and teeth from Khok Sung are morphologically similar to those observed from recent Axis axis . This suggests a morphological stasis in the evolution of antlers and teeth for this species.

Based on our observation on the extant comparative material of Axis axis (e.g., the specimens MNHN-ZMO-1901-547, MNHN-ZMO-1988-153, ZSM-1951-70, and ZSM-1958-88), we thus demonstrate some dental morphological variation within species. The m3 of Axis axis appears more morphologically variable than the other molars, such as the more or less developed posterior talonids and the presence/absence of back fossae. The cheek teeth of extant Axis axis are relatively similar to those of Axis porcinus (e.g., the specimens MNHN-ZMO-1904-60, MNHN-ZMO-1962-4188, ZSM-1968-493, and ZSM-1969-63). However, Axis axis differs from Axis porcinus in having less developed anterior cingulids on the lower molars and the presence of back fossae on the m3. Recent Axis axis represents an intermediate size between Axis porcinus and two cervid species ( Panolia eldii and Rusa unicolor ) (Tab. 14). Axis axis from Khok Sung also follows the size tendency of recent populations (Figs 17 and 18).

Compared to other Pleistocene cervid species, the cheek teeth of Axis axis from Khok Sung are smaller than those of Axis shansius from Anhui and Yunnan (China) and of Axis javanicus from Ngandong and Buitenzorg in Java and Carnul Cave in India, but are larger than those of Axis lydekkeri from Trinil H. K. (Java) (Figs 17 and 18). Although, Axis javanicus is closely related to or even synonymous with Axis axis according to Meijaard and Groves (2004), it is considered as a valid species due to studies of the geometric morphometric analysis performed on the teeth ( Gruwier et al. 2015). According to the scatter diagrams of the dental sizes (Figs 17 and 18), Thum Wiman Nakin and Thum Prakai Phet fossil teeth assigned to Axis porcinus ( Tougard 1998, Filoux et al. 2015) are much larger than their extant populations and those from Khok Sung. Although the Pleistocene hog deer probably show clinal variation in size ( Bergmann’s rule) in re sponse to colder climates. The fossil teeth attributed to Axis porcinus from Thum Wiman Nakin and Thum Prakai Phet, identified by Tougard (1998) and Filoux et al. (2015), possibly reveal a double size (or more) of the recent population. We suggest that these fossils likely belong to either other larger or new cervid species that lived during the Pleistocene across mainland Southeast Asia. We also cast doubt on the occurrence of Axis porcinus in the Middle Pleistocene of Boh Dambang, Cambodia ( Demeter et al. 2013). The existence of Axis porcinus in Southeast Asia during the Middle Pleistocene is still doubtful.