Isanichthys latifrons ( Woodward, 1893 )

Deesri, Uthumporn, Lauprasert, Komsorn, Suteethorn, Varavudh, Wongko, Kamonlak & Cavin, Lionel, 2014, A new species of the ginglymodian fish Isanichthys from the Late Jurassic Phu Kradung Formation, northeastern Thailand, Acta Palaeontologica Polonica 59 (2), pp. 313-331 : 326-327

Isanichthys latifrons ( Woodward, 1893)

Material.— BMNH P.6838, subcomplete individual; BMNH P.6840, isolated skull bones; BMNH P. 6841 (holotype) isolated but articulated skull bones and scales; BMNH P. 45620, head; from Middle Jurassic of the United Kingdom (for details see Cavin 2010) .

Emended diagnosis.— Isanichthys with most of the dermal ossifications of the skull ornamented with tubercles of ganoin; skull roof proportionally short, being approximately 1.5 times longer than wide; parietals asymmetrical; preorbital region reduced; ca. 12 suborbitals arranged in a mosaic pattern; semi-tritorial dentition; two pairs of extrascapulars; toothed maxilla.

Remarks.— Isanichthys latifrons ( Woodward, 1893) was originally described as Lepidotes latifrons by Woodward (1893) on the basis of material from the Oxford Clay of Northamptonshire, UK. Woodward (1893) compared the skull of this species to the Early Jurassic “ Dapedius ” (= Dapedium ), to which it was thought to be closely related. Later, Jain (1983) discussed some characters of this species.

Isanichthys latifrons possesses characters of the genus Isanichthys such as the strongly ornamented bones of the skull roof, the frontal only slightly narrower anteriorly than posteriorly, the frontal less than 2.5 times longer than the parietal, two supraorbitals, the cheek region completely covered by bones, the preopercle slightly curved, the maxilla forming a thin blade with a posterior rounded plate-like part, a posttemporal fossa and an oral sensory canal, ratio of skull length to orbit length greater than 6, and the quadrate situated below the orbit. Moreover, based on the proportions of the skull and the reconstruction figured by Jain (1983), the anterior infraorbital would have been deep, and the anterior supraorbital would have closed the orbit anteriorly and should have contacted two infraorbitals, three other characters diagnostic of Isanichthys . In contrast to the other Isanichthys species, I. latifrons bears small tubercles of ganoin of its dermal skull bones, and other specific characters mentioned in the diagnosis above.