A new Ginglymodi (Actinopterygii, Holostei) from the Late Jurassic–Early Cretaceous of Thailand, with comments on the early diversification of Lepisosteiformes in Southeast Asia

ABSTRACT

A new ginglymodian fish, Khoratichthys gibbus, gen. et sp. nov., is described based on the impression of a single articulated fish preserved on a sandstone slab from the Late Jurassic–Early Cretaceous Phu Kradung Formation, northeastern Thailand. Khoratichthys gibbus is characterized by a distinct humpbacked body with elongate posterior spines on the dorsal ridge scales; the cheek is completely covered by bone; it has few infraorbitals, the elongate anterior-most one shows a tiny contact with the orbit, and six suborbitals arranged in one row; the opercule is rectancular in shape; the preopercule is narrow and regularly curved; and the interopercule large. A cladistic analysis including the type species of 25 ginglymodian genera indicates that Khoratichthys is the basal-most Lepisosteiformes, in an unresolved position with Neosemionotus and Lophionotus. This taxon provides a new evidence of the high diversity of ginglymodian fishes in the Phu Kradung Formation. A high taxic diversity of ginglymodians in Middle Jurassic–Early Cretaceous of southern Asian (excluding India) freshwater environments is observed, indicating that this clade occupied a major position in freshwater fish assemblages.

http://zoobank.org/urn:lsid:zoobank.org:pub:AE3056BF-0C4A-421F-B517-3A4BC777A3E1

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Citation for this article: Deesri, U., P. Jintasakul, and L. Cavin. 2016. A new Ginglymodi (Actinopterygii, Holostei) from the Late Jurassic–Early Cretaceous of Thailand, with comments on the early diversification of Lepisosteiformes in Southeast Asia. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1225747.

ACKNOWLEDGMENTS

We thank Y. Thasod, R. Hunta, and NRIPM staff for assisting us during a study visit to the NRIPM. We also thank S. Suteethorn (Palaeontological Research Centre and Education) for his dedicated help to greatly improve the photographs of all specimens, and two anonymous reviewers for constructive suggestions for improvement of the manuscript. U.D. was supported by a research fellowship grant 2015 from the French Embassy of Thailand and by the Mahasarakham University Development Fund. Specimens collected in 1997 for this study were under the supervision of the Northeastern Research Institute of Petrified Wood and Mineral Resources, Nakhon Ratchasima Rajabhat University, Nakhon Ratchasima, Thailand.