Crocodylus cf. siamensis Schneider, 1801

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 : 55-56

Taxon classification Animalia Crocodylia Crocodylidae

Crocodylus cf. siamensis Schneider, 1801

Referred material.

A fragmentary cranium, DMR-KS-05-03-30-30; a dentary fragment with one tooth, DMR-KS-05-03-21-1; five isolated teeth-DMR-KS-05-03-00-19, DMR-KS-05-03-14-3, DMR-KS-05-03-22-22, DMR-KS-05-04-06-3, and DMR-KS-05-04-29-10; three osteoderms-DMR-KS-05-03-29-57, DMR-KS-05-03-29-58, and DMR-KS-05-03-27-25.

Material description.

Skull and dentition: DMR-KS-05-03-30-30 is a slightly deformed skull preserving a nearly complete premaxilla, maxilla, nasal, and palatine process (Fig. 35A, B), and a partial palatine at the ventral part. The minimum length of the skull is 315 mm. The external naris is wide, dorsally directed, and presumably subcircular in outline (Fig. 35A). The nasal becomes narrower at the nearly premaxillary-maxillary suture and tapers into a point at the posterior rim of the naris. The premaxilla is broken anteriorly at the hole for the reception of the first dentary alveolus. The premaxilla contains at least four teeth on each side. The second one is the largest tooth in the premaxillary rows, regularly corresponding to the position of a large alveolar hole in dorsal view. A short premaxillary process extends to the second maxillary alveolus centrally or the first interalveolus laterally in ventral view (Fig. 35B). The premaxillary–maxillary suture is characterized by distinct notches. A maxilla comprises 14 alveoli, with the largest tooth crown (44.3 mm high) positioned at the fifth dentary alveolus. The width of the skull at the fifth maxillary tooth is 171.8 mm (the maximum width of the preserved skull). The width of the skull at the diastema between the last premaxillary tooth and the first maxillary tooth (the minimum width of the preserved skull) is 98.9 mm. Many small foramina in front of the alveoli are situated on both the premaxilla and the maxilla. Along the anterior to posterior maxillary rims, the tooth row is slightly convex until ending at the eighth or ninth alveolus. Teeth are characterized by their conical forms and striated surfaces. However, they are highly variable in shape and size, in relation to the position along the tooth row. The teeth of crocodyles are either slender and pointed or short and blunt (Fig. 35C) but much more massive than those of gharials. Asymmetrical surfaces of the tooth are divided by two prominent longitudinal ridges that are positioned anteriorly and posteriorly.

Osteoderms: two nearly complete specimens (Fig. 35 D–G) and one small fragment are characterized by rectangular shapes, wider than long (about 5-6 cm long and 7-8 cm width), and slightly flat to convex and irregular edges with small spiny outgrowths. A short median keel does not extend far anteriorly or posteriorly (Fig. 35D, F). The external surface has several large and rounded to elliptical pits on the dorsal part and fewer small foramina and striae with surrounding fibrous patterns on the ventral part (Fig. 35E, G). These specimens differ from Gavialis cf. bengawanicus ( Martin et al. 2012) in the same locality by their more ornamented pits and more irregular surfaces on the dorsal surface.

Taxonomic remarks and comparisons.

The specimen DMR-KS-05-03-30-30 is a crocodilian cranium with a possible maximum length up to 50 cm. All morphological characters of the Khok Sung crocodiles are congruent with the extant fresh water crocodile, Crocodylus siamensis , as well as with its fossils recovered from the Early and Middle Pleistocene of Java (Trinil H. K., Kedung Brubus, and Kedung Lumbu) ( Delfino and de Vos 2010). However, the Khok Sung cranium preserves only the anterior midway portion of the skull and does not allow some morphological access to other important parts (e.g., lacrymals, jugals, and pterygoids). We thus attribute this material to Crocodylus cf. siamensis .