Ocadia Gray, 1870

Takahashi, Akio, Ōki, Kimihiko, Ishido, Takahiro & Hirayama, Ren, 2013, A new species of the genus Ocadia (Testudines: Geoemydidae) from the middle Miocene of Tanegashima Island, southwestern Japan and its paleogeographic implications, Zootaxa 3647 (4), pp. 527-540 : 529

Ocadia Gray, 1870

Type species. Ocadia sinensis (Gray, 1834) .

Included species. Ocadia sinensis (Gray, 1834) ; O. nipponica Hirayama et al., 2007 .

Revised diagnosis. Modified on the basis of Smith (1931), Bourret (1941), Ernst and Barbour (1989), Hirayama et al. (2007), and this study: medium to large–sized hingeless geoemydids with following combination of character states: hexagonal neural plates short–sided in front; posterior margin of the carapace unserrated; second and third vertebral scutes frequently showing nearly rectangular in shape, as long as wide; the entoplastron intersected by the humero–pectoral sulcus; the plastral buttresses moderately developed, extending to half way of the costal plates; median length of the gular shorter than the interhumeral sulcus and the gular often isolated from the entoplastron; enlarged upper and lower triturating surface decorated by the lingual ridges; the upper triturating surface with a denticulate median ridge; and the foramen palatinum posterius small.

Remarks. Recent molecular phylogenetic analyses have shown that the genus Ocadia is included in a clade with Chinemys spp. and Mauremys japonica and that these taxa form another more inclusive clade with the remaining living species of Mauremys ( Mauremys sensu lato, Honda et al. 2002; Barth et al. 2004; Feldman and Parham 2004; Spinks et al. 2004; Sasaki et al. 2006; Jiang et al. 2011). However, no synapomorphic morphological character states are known for the two clades (e.g., Honda et al. 2002; Hirayama et al. 2007). Actually, because Ocadia differs much from Chinemys and Mauremys in several skull and shell characters (e.g., McDowell 1964; Hirayama 1985; Gaffney and Meylan 1988; Yasukawa et al. 2001), we retain the genus Ocadia for disclosing its past species diversity from paleontological view in the present study.