Sus barbatus Mueller , 1838

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 : 23-25

Taxon classification Animalia Artiodactyla Suidae

Sus barbatus Mueller, 1838

Referred material.

A left maxillary fragment with P3-M2, DMR-KS-05-04-19-2; two left M2-DMR-KS-05-04-19-5 and DMR-KS-05-03-18-23 (posterior portion); two right M3-DMR-KS-05-04-03-4 and DMR-KS-05-04-19-4 (anterior portion); two mandible with two tooth rows-DMR-KS-05-03-15-1 (right: i1, i2, c1, p2, and p3 and left: i1, i2, c1, and p2-m2) and DMR-KS-05-04-19-1 (right: i1, i2, c1, and p1-m3 and left: i1, i2, c1, and p1-p4); a left posterior fragment of m3, DMR-KS-05-04-19-3; a right humerus, DMR-KS-05-03-26-8.

Material description.

Upper dentition: DMR-KS-05-04-19-2 is a maxillary tooth row preserving a slightly worn P3 to M2 (Fig. 13A). The P3 and P4 show Sus -like patterns with distinctly pre- and poststyles on the buccal side. On the P3, the paracone is well-developed and the postcrista projects posterobuccally. On the P4, three main cusps (protocone, paracone, and metacone) are distinct and the protofossa is present. Upper molars are unworn to slightly worn and exhibit distinct main (protocone, paracone, metacone, tetracone, and pentacone) and accessory (tetrapreconule, pentapreconule, and ectoconule) cusps. The posterior cingulum on the M2 is more developed than on the M1 (Fig. 13 A–C). The M3 (DMR-KS-05-04-03-4: Fig. 13D) is unworn and subtriangular in outline and has a distinct anterior cingulum, pentacone, and pentapreconule and bulky accessory cusps. Another M3 (DMR-KS-05-04-19-4) does not preserve a posterior part but has well-developed main cusps, anterior cingulum, median valley, tetrapreconule, and ectoconule (Fig. 13E). The cheek teeth of DMR-KS-05-04-19-4 are larger than those of DMR-KS-05-04-03-4.

Mandible and lower dentition: DMR-KS-05-03-15-1 is incomplete, lacking the body and ascending ramus, broken posterior to the right p3 and to the left m2 (Fig. 13F, G) (for measurements, see Appendix 3). The mandible is inflated. The small mental foramen is present below the diastema between p1 and p2. Only the i3 and p1 are missing. The left p2 is not aligned along the cheek tooth row due to the deformation. The specimen DMR-KS-05-04-19-1 preserves a complete symphysis and a right body with the tooth row. The ramus is broken away (Fig. 13H, I). The mandibular body is successively inflated. The mental foramina are situated below the diastema between p1 and p2. For the specimen DMR-KS-05-04-19-1, the teeth are complete and moderately to heavily worn but the third incisors are missing.

Lower incisors show a chisel-like appearance with long roots. The i2 is larger than the i1. Lower canines are slender and pointed, and curve backward. The lower canines of the mandible DMR-KS-05-03-15-1 belong to a male individual because of a more sharply triangular section ( Hillson 2005) (Fig. 13F). The mandible DMR-KS-05-04-19-1 possesses a female canine characterized by more rounded cross-sections and well-developed roots ( Hillson 2005) (Fig. 13H). The lower canines of the male specimen are more laterally inclined (about 30° from the cheek teeth) than those of the female individual (about 15°). The cross-section outlines of male canines (DMR-KS-05-03-15-1) are of the “verrucosic” type in which the posterior side is narrower than the labial one (Fig. 13F). All lower cheek teeth exhibit bunodont patterns with accessory tubercles, like in Sus . The lower cheek teeth increase in size from anteriorly to posteriorly (Tab. 10). Lower premolars are slightly to moderately worn. The p1 is unicuspid. Other premolars are tricuspid. All cuspids are sharp. The highest cuspid on the premolars is the metaconid. Lower molars are moderately to heavily worn and rectangular in outline (Fig. 13 F–J). The lower molars show complex occlusal patterns with well-developed main cuspids (protoconid, metaconid, hypoconid, entoconid, and pentaconid) and a bulky median column (hypopreconulid). The m2 is much larger and has a more developed posterior cingulid than the m1 (Fig. 13F, H). The m3 (DMR-KS-05-04-19-1) is elongated posteriorly (Fig. 13H). It has a well-developed talonid with bulky main and accessory cuspids (pentaconid, pentapreconulid, hexaconid, heptaconid). Another isolated posterior fragment (talonid) of the m3 (DMR-KS-05-04-19-3) is also elongated, as long as that of DMR-KS-05-04-19-1. This specimen exhibits smooth occlusal surfaces with wear and well developed main and accessory cuspids (Fig. 13J). The m3 is longer than the combination of m1 and m2 (Tab. 10).

Postcranial bone: DMR-KS-05-03-26-8 is a complete humerus (Fig. 13 K–N), characterized by its prominent tubercle slightly overhanging the large bicipital groove (Fig. 13K), proximal part becoming wider than long (Fig. 13K), mesially flat and laterally compressed shaft, distinct deltoid ridge starting at the mid-shaft (Fig. 13L, M), large supinator ridge and supratrochlear foramen (Fig. 13M), shallow musculo-spiral groove (Fig. 13N), and small deltoid tuberosity (Fig. 13N). The size and morphology of the humerus DMR-KS-05-03-26-8 resemble those of recent Sus barbatus (for measurements, see Appendix 1).

Taxonomic remarks and comparisons.

We compare our material to some Pleistocene Southeast Asian suid species, although only two distinct suid species, Sus scrofa and Sus barbatus , are known from many Pleistocene localities of mainland Southeast Asia. The sizes of the Khok Sung material are obviously larger than those of Pleistocene and extant Indonesian suids ( Sus brachygnathus , Sus macrognathus , Sus verrucosus , and Sus celebensis ) (Tab. 10). The Khok Sung suid material is comparable in size to Sus scrofa and Sus barbatus . The two suid mandibles from Khok Sung also show some distinctive taxonomic characters of Sus scrofa and Sus barbatus . For example, the mandible is not laterally enlarged or swollen and the diastema from p1 to p2 is longer than from c1 to p 1, which are only characteristics of some species of Sus : Sus scrofa , Sus celebensis , and Sus barbatus ( Groves 1997). The lower premolar rows on the mandibles are aligned along the mandible, unlike Sus verrucosus and Sus celebensis in which the premolar rows diverge anteriorly ( Groves 1997).

However, it is difficult to distinguish Sus scrofa from Sus barbatus only based on the cheek teeth because both species overlap in size (Tab. 10) and show almost similar dental patterns. The main differential characters between Sus scrofa and Sus barbatus are defined on the basis of the shape of lower canines in male individuals, whether the outline of the cross-section is of the “scrofic” (i.e. the posterior side is wider than the labial one ( Sus scrofa )) or “verrucosic” ( Sus barbatus ) type ( Badoux 1959, Hardjasasmita 1987). Similarly, this distinctive feature is demonstrated by the lower male canine index (the width of labial surface as a percentage of the width of posterior surface) ( Groves 1981, 1997). The canine index ranges from 61.5 to 109.1 for recent Sus scrofa and from 105.6 to 144.4 for extant Sus barbatus ( Groves 1981: table. 1). The lower canines of the male mandible DMR-KS-05-03-15-1 show the verrucosic type with the canine index of Sus barbatus (for the detailed calculation see Tab. 11). We also provide the canine index of the female specimen DMR-KS-05-04-19-1 in Tab. 11. A minor distinctive character between Sus scrofa and Sus barbatus is differences of the posterior accessory median cuspid (pentapreconulid) on the talonid. The pentapreconulid on the m3 is small or absent in Sus barbatus ( Badoux 1959). For other molar characters, Sus barbatus shows more complex patterns with accessory tubercles and more rugose enamel than in Sus scrofa ( Tougard 1998, Bacon et al. 2011). However, the latter character is useless to make a distinction between both suid species according to our observations on the recent material of Sus barbatus . The enamel surfaces of the molars in Sus barbatus are often smooth or even sometimes smoother than in Sus scrofa .

The female mandible (DMR-KS-05-04-19-1) and other isolated teeth are assigned to Sus barbatus according to those described features. We also suggest that Pleistocene Sus barbatus probably shows evidence of sexual size dimorphism because the female specimen DMR-KS-05-04-19-1 is markedly smaller than the male specimen DMR-KS-05-03-15-1, as seen in the recent population.