DOI: 10.15468/xtghak
title: First occurrence of brachyopid temnospondyls in Southeast Asia and review of the Mesozoic amphibians from Thailand

description: This dataset contains the digitized treatments in Plazi based on the original journal article Nonsrirach, Thanit, Manitkoon, Sita, Lauprasert, Komsorn (2021): First occurrence of brachyopid temnospondyls in Southeast Asia and review of the Mesozoic amphibians from Thailand. Fossil Record 24 (1): 33-47, DOI: 10.5194/fr-24-33-2021, URL: http://dx.doi.org/10.5194/fr-24-33-2021Abstract. The non-marine Mesozoic sedimentary rocks of Thailand, which consist of the Indochina block and the Sibumasu block, have yielded several terrestrial and aquatic vertebrate fossils, but only few amphibian remains have been reported. Here, we present an overview on the Thai amphibian palaeo-diversity based on the literature, re-examination of published material, new findings, and unpublished material. Thai amphibian fossil remains are assigned to Stereospondyli (Cyclotosauridae, Plagiosauridae, and Brachyopoidea) and Anura and were discovered from four formations, ranging from the Upper Triassic to Lower Cretaceous of Thailand. The occurrence of Brachyopidae in Thailand, which are related to Chinese forms, supports the previous hypothesis of physical connections between the Indochina blocks and the Sibumasu block during the Mesozoic era.1 IntroductionThe amphibians of the Paleozoic and the Mesozoic can be dived into three major clades: the Seymouriamorpha, the Lepospondyli, and the Temnospondyli (Vitt and Caldwell, 2014). Basal members of temnospondyls were the most diverse and most successful group of amphibians in the Paleozoic, which lived during the Mesozoic Era (Damiani and Rubidge, 2003; Schoch, 2014). Temnospondyls are commonly retrieved in the tetrapod assemblages from Triassic continental deposits such as fluvial and lacustrine environments (Schoch and Milner, 2000; Dias-da-Silva and Dias, 2013).We present here an update of the amphibian continental fossil record during the Mesozoic in Thailand. The Mesozoic rocks of Thailand consist of two sub-continent blocks. The western part, called “Shan-Thai block” or “Sibumasu block”, includes the eastern part of Myanmar and northern, western, and southern parts of Thailand as well as the western peninsula of Malaysia (Fig. 1). The eastern part is the Indochina block, which includes northeastern and eastern parts of Thailand, southern parts of Laos and Cambodia, and the western part of Vietnam (Metcalfe, 1996; Buffetaut and Suteethorn, 1998; Racey, 2009). The Mesozoic rocks in the northeastern part of Thailand, which belong to Indochina, consist of a non-marine red bed sequence deposited in a continental environment (Racey et al., 1996; Racey, 2009). This block consists of seven formations considered Upper Triassic to Cretaceous in age based on invertebrate and vertebrate remains as well as palynomorphs (Meesook et al., 1995; Racey et al., 1996). However, fossils of Thai amphibians (i.e., Cyclotosaurus cf. posthumus, Plagiosauridae, Temnospondyli indet., and Anura) were discovered only from three formations of the Indochina block (Ingavat and Janvier, 1981; Suteethorn et al., 1988; Buffetaut et al., 1994a; Srisuk, 2002, 2005) which are as follows.1. The Huai Hin Lat Formation is mainly formed by lacustrine bituminous limestone and shales (Buffetaut and Suteethorn, 1998). It is considered Upper Triassic based on palynomorphs, plant macro-remains, conchostracans, and vertebrate remains (Kobayashi, 1975; Racey et al., 1996; Buffetaut and Suteethorn, 1998; Department of Mineral Resources, 2014). The vertebrate assemblages from the Huai Hin Lat Formation consist of actinopterygian fishes (Martin, 1984), lungfish (Martin and Ingavat, 1982), temnospondyls (Ingavat and Janvier, 1981; Suteethorn et al., 1988), and phytosaurs (Buffetaut and Ingavat, 1982).2. The Phu Kradung Formation consists of sequences of sandstone, siltstone, and mudstone deposited on a lacustrine-dominated alluvial floodplain environment (Meesook, 2000; Racey, 2009). This formation is assigned to Upper Jurassic based on palynomorphs, bivalves (Racey et al., 1994, 1996; Meesook, 2000), and vertebrate remains which consist of hybodont sharks (Cuny et al., 2005), actinopterygians (Cavin et al., 2003; Cavin and Suteethorn, 2006), temnospondyls (Buffetaut, et al., 1994a), turtles (Tong et al., 2009), crocodiles (Buffetaut and Ingavat, 1980), and dinosaurs (Buffetaut, et al., 2014).3. The Sao Khua Formation consists of sequences of red clays, sandstones, and conglomerates deposited on a floodplain with a meandering river environment (Buffetaut and Suteethorn, 1998). This formation is assigned to Lower Cretaceous based on palynomorphs, bivalves (Racey et al., 1994, 1996; Meesook, 2000), and vertebrate remains, i.e., hybodont sharks (Cuny et al., 2007), actinopterygian fishes (Cavin et al., 2009), anurans (Srisuk, 2002, 2005), turtles (Tong et al., 2009), crocodilians (Buffetaut and Ingavat, 1980), and dinosaurs (Buffetaut and Suteethorn, 1999).In the Sibumasu block of the southern peninsula of Thailand, temnospondyls were discovered in the Klong Min Formation (Buffetaut et al., 1994b, c), which is formed by limestone and grey to brown clays, indicating a lacustrine depositional environment (Tong et al., 2002). The Klong Min Formation is considered Middle or Upper Jurassic in age, based on charophytes and vertebrate remains (Buffetaut et al., 1994b; Tong et al., 2002; Girard et al., 2020). The vertebrate assemblages of this formation consist of hybodont sharks, actinopterygian fishes, lungfish, turtles, and crocodiles (Buffetaut et al., 1994b, c; Tong et al., 2002).Figure 1. Mesozoic amphibian outcrops from Thailand (symbol); locality in Huai Hin Lat Formation (Upper Triassic), Khlong Min Formation (Middle or Upper Jurassic), Phu Kradung Formation (Upper Jurassic), and Sao Khua Formation (Lower Cretaceous).Although thousands of vertebrate remains have been found, few amphibian remains have been reported. More recently, new specimens of amphibians (intercentra and a posterior part of a skull) were collected from new Mesozoic localities in Thailand, i.e., Huai Nam Aun locality, Phu Noi locality, and Khao Wong locality (Laojumpon et al., 2014; Chanthasit et al., 2019). In order to understand the diversity and biogeography of Thai Mesozoic amphibians, we describe and re-check the taxonomic status of all amphibian remains housed in the collections of the Sirindhorn Museum (SDM, Kalasin Province) and the Palaeontological Research and Education Centre of Mahasarakham University (PRC, Mahasarakham Province). The relationships between these amphibians and their Asian relatives are used in a palaeobiogeographical framework for a better reconstruction of the physical connections in Southeast Asia.