Shark faunas from the Late Jurassic—Early Cretaceous of northeastern Thailand

Gilles Cuny,Tida Liard,Uthumporn Deesri,Varavudh Suteethorn,Suchada Khamha,Romain Liard

doi:10.1007/s12542-013-0206-0

Gilles Cuny, Tida Liard + Show 4 more

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https://doi.org/10.1007/s12542-013-0206-0

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Abstract

A revision of the freshwater shark fauna from the Phu Kradung Formation in NE Thailand allows the recognition of a new species of Acrodus, which represents the youngest occurrence of the genus and confirms its displacement in freshwater environments after the Toarcian. The rest of the shark fauna includes teeth of Hybodus sp., aff. Hybodus sp., hybodontid dermal denticles, Jiaodontus sp., Lonchidion sp. A, Lonchidion sp. B, Heteroptychodus cf. H. kokutensis and dorsal fin spines. The presence of Jaiodontus and of unusual hybodontid dermal denticles suggests a Jurassic age for most of the Phu Kradung Formation, whereas the presence of Heteroptychodus suggests an Early Cretaceous age for the top of the Formation. However, the age of the Phu Kradung Formation is still uncertain, with contradictory signals coming from palynology, detrital zircon thermochronology and vertebrate palaeontology. In any case, it appears that this is the oldest occurrence of the genus Heteroptychodus, and suggests a Thai origin for this genus, which may have replaced Acrodus in the Thai freshwater palaeoecosystems. Together with Acrodus, the presence of Lonchidion sp. A suggests some European affinities for the shark fauna from the Phu Kradung Formation.

Highlights

Since 1990, the Khorat Group (Late Jurassic—Early Cretaceous in age) has yielded rich assemblages of freshwater hybodont sharks, which were recovered from three formations: the Phu Kradung, Sao Khua and Khok Kruat Formations (Cuny et al 2007)
A revision of the freshwater shark fauna from the Phu Kradung Formation in NE Thailand allows the recognition of a new species of Acrodus, which represents the youngest occurrence of the genus and confirms its displacement in freshwater environments after the Toarcian
The age of the Phu Kradung Formation is still uncertain, with contradictory signals coming from palynology, detrital zircon thermochronology and vertebrate palaeontology

Summary

Introduction

Since 1990, the Khorat Group (Late Jurassic—Early Cretaceous in age) has yielded rich assemblages of freshwater hybodont sharks, which were recovered from three formations (from bottom to top): the Phu Kradung, Sao Khua and Khok Kruat Formations (Cuny et al 2007). In 2008, the discovery of a new locality in Kalasin Province, Phu Noi, led to the discovery of shark teeth in conglomeratic sandstones of the Phu Kradung Formation, the preservation of which was better than at any other sites discovered in this formation so far. Its thickness varies from 1,200 m in the basin centre to around 500 m on its southern flanks (Racey 2009) It consists of fluvial sandstones, siltstones and mudstones, and is dated as either Late Jurassic based on fossil vertebrate evidence (Buffetaut et al 2001; Buffetaut and Suteethorn 2007; Tong et al 2009a) or Early Cretaceous on the basis of palynology (Racey and Goodall 2009) and detrital zircon thermochronology (Carter and Bristow 2003). All of the sites listed below are located in the upper part of the Phu Kradung Formation (Fig. 1)

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