A new species of the ginglymodian fish Isanichthys (Actinopterygii, Holostei) from the Late Jurassic Phu Kradung Formation, northeastern Thailand

Abstract

A new ginglymodian fish, Isanichthys lertboosi, is described from the Phu Kradung Formation, north-eastern Thailand, a freshwater deposit of probable Late Jurassic age. The species is represented by four specimens, from the Phu Noi locality, associated with a rich fauna of sharks, turtles, crocodiles, and theropod and sauropod dinosaurs. One specimen is an isolated braincase, which provides characters rarely observed in extinct ginglymodians. The species is referred to the genus Isanichthys, a taxon originally described on the basis of a single specimen from the Phu Nam Jun locality, a slightly younger site approximately 75 km from Phu Noi. Isanichthys is mainly distinguished by frontals slightly narrower anteriorly than posteriorly, two anterior infraorbitals not in contact with the orbit, reduced preorbital region, and a small orbit and a cheek region completely covered by bones. The new species is characterized, among other characters, by a dermal component of the sphenotic visible on the cheek, one pa...