A new Lepisosteiformes (Actinopterygii: Ginglymodi) from the Early Cretaceous of Laos and Thailand, SE Asia

Abstract

A new genus and new species of ginglymodian is described from the Aptian Grès supérieurs Formation of the Savannakhet Basin, Laos (Lao People's Democratic Republic), found at the Ban Lamthouay locality. The fish is known from a single isolated head, which shows enough diagnostic characters to characterize a new taxon. It represents the first named actinopterygian fish from the Mesozoic of Laos. Among the derived characters are a very short and deep head, a series of very deep anterior infraorbitals, and a mosaic arrangement of the suborbitals. Recognition of this new form led us to identify isolated bones previously found in the Thai Khok Kruat Formation in Thailand, a lateral equivalent of the Grès supérieurs Formation. Two localities, Ban Saphan Hin and Khok Pha Suam, have yielded remains, in particular bones of the skull roof and of the circumorbital series as well as a partial postcranial body, assignable, with caution, to the new genus. When included in a cladistic analysis, the new taxon is placed at the base of the lepisosteoid lineage, together with Isanichthys known from an older formation in Thailand. The phylogenetic pattern obtained differs in some details from previous analyses and points out the pivotal role that some taxa play in the reconstruction of the phylogenies of ginglymodians. This new taxon enriches the diverse Late Jurassic–Early Cretaceous ginglymodian assemblage in South-east Asia, which surprisingly shows no evidence of teleosts.

http://zoobank.org/urn:lsid:zoobank.org:pub:70564BE0-939C-4217-9D82-9E51AA298A8C

Keywords:

• systematics
• Holostei
• Mesozoic
• stratigraphy
• freshwater environment

Acknowledgements

The authors thank staff of the Sirindhorn Museum, the Palaeontological Research and Educational Center (PRC) of Mahasarakham University, the Department of Mineral Resources (DMR) of Thailand and the Savannakhet Dinosaur Museum who participated in the fieldwork. Part of this study was supported by the Swiss National Science Foundation (grant 200021-113980 to LC and UD), the International Scientific Coordination Network (GDRI) PalBioDivASE (UD), the Laotian Ministry of Sciences and Technology, the Savannakhet Province, and the ‘Formation et Recherche au Laos’ Association. We thank P. Richir, P. Sayarath, P. Taquet and R. Vacant for assistance during fieldwork. We are grateful to Alison Murray (University of Alberta) and an anonymous referee for their thorough and constructive reviews.

Supplemental material

Supplemental material for this article can be accessed at: https://doi.org/10.1080/14772019.2018.1426060

Additional information

Funding

Part of this study was supported by the Swiss National Science Foundation (grant 200021-113980 to LC and UD)