Mesozoic vertebrates from Thailand 83 The biogeographical significance of the Mesozoic vertebrates from Thailand Eric Buffetaut1 and Varavudh Suteethorn2 1UMR CNRS 5561, Université de Bourgogne, France# Present address: 16 cour de Liégat, 75013 Paris, France 2Geological Survey Division, Department of Mineral Resources, Rama VI Road, Bangkok 10400, Thailand Key words: Thailand, Mesozoic, vertebrates, amphibians, reptiles, biogeography Abstract brates, ranging in age from Late Triassic to late Early Cretaceous (for a recent review of the di- Mesozoic non-marine vertebrate faunas from Thailand nosaurs, see Suteethorn et al#, 1995), This is by (mainly from the Indochina block) range in age from Late Triassic to late Early Cretaceous The oldest known assem- far the best record for that time interval in SE blage, from the Huai Hin Lat Formation, is Norian It in- Asia, and it allows a reconstruction of vertebrate cludes fishes, amphibians and reptiles very similar to those faunal history in that part of the world over a from the Upper Triassic of Central Europe, and indicates period of more than 100 million years, The pur- that dispersal of continental vertebrates across Eurasia was pose of this brief review is to discuss the easy in the Late Triassic A slightly younger (Rhaetian) prosauropod dinosaur is biogeographically less significant, palaeobiogeographical significance of the vari- although it may be related to Chinese forms Jurassic verte- ous Mesozoic vertebrate assemblages hitherto brates are known from both the Indochina block (Phu discovered in Thailand, Kradung Formation) and the Shan-Thai block Resem- blances between the assemblages from both areas suggest that they were already in contact in the Jurassic Similarities with Jurassic vertebrates from China indicate links with General geological setting more northerly parts of Asia The Lower Cretaceous (pre- Aptian) Sao Khua Formation contains a vertebrate fauna It is now generally accepted that Thailand con- which seems to be older than most Cretaceous assemblages sists of two continental blocks or microconti- known from other parts of Asia, and probably corresponds to a phase of relative isolation of Asia It includes dinosaurs nents (Fig,1), the eastern part (with, notably, the which may be close to the ancestry of groups which later Khorat Plateau where most Mesozoic vertebrate played an important part in Asian and North American as- localities are) belonging to the Indochina block, semblages, such as tyrannosaurids and ornithomimids while the western part (including the southern Some of the Sao Khua sauropods may be related to the poorly known Upper Cretaceous sauropods of Mongolia peninsula) is part of a terrane variously called and China The Aptian-Albian Khok Kruat Formation has Shan-Thai or Sibumasu (see Metcalfe, 1996, yielded a freshwater shark also known from the Lhasa block for a recent review), The Indochina block seems of Tibet, as well as the ceratopsian dinosaur Psittacosaurus, to have sutured to South China in the Carbonif- which was widespread in Asia during the Early Cretaceous erous (Metcalfe, 1996), The timing of the colli- It also contains remains of iguanodontid dinosaurs which are probably immigrants from Europe and show that by the sion of the Shan-Thai block with Indochina and late Early Cretaceous the isolation of Asia had ended South China is still debated (Late Permian to Triassic according to Metcalfe, 1996; as late as Late Jurassic according to Stokes et al#, 1996), Introduction The Mesozoic non-marine vertebrates found in Thailand (Table 1) can thus provide some evi- In the last twenty years, Thailand has yielded a dence concerning the late stages of the accre- number of Mesozoic non-marine fossil verte- tion history of these terranes, Biogeography and Geological Evolution of SE Asia, pp 83-90 Edited by Robert Hall and Jeremy D Holloway © 1998 Backhuys Publishers, Leiden, The Netherlands 84 E# Buffetaut and V# Suteethorn Upper Triassic: the vertebrate assemblage from the Huai Hin Lat Formation The Huai Hin Lat Formation of the Khorat Pla- teau consists mainly of lacustrine bituminous limestones and shales, It is Upper Triassic, prob- ably Norian, on the basis of plant macro-remains (Konno and Asama, 1973), palynomorphs (Haile, 1973; Racey et al#, 1996), conchostracans (Kobayashi, 1975) and vertebrates (review in Buffetaut et al#, 1993), The vertebrate assemblage from the Huai Hin Lat Formation, which consists of both isolated elements and partly articulated skeletons, in- cludes actinopterygian fishes (Martin, 1984), lungfishes (Martin and Ingavat, 1982), amphib- ians (Cyclotosaurus: Ingavat and Janvier, 1981; plagiosauroid indet: Suteethorn et al#, 1988), tur- tles (Proganochelys: Broin et al#, 1982, Broin, 1984), and phytosaurs, including a Belodon-like form and Mystriosuchus (Buffetaut and Ingavat, 1982; Buffetaut et al#, 1993), From a biogeographical point of view, the freshwater vertebrate assemblage from the Huai Hin Lat Formation is remarkable in that it closely resembles the classic vertebrate fauna from the Norian of Germany (Stubensandstein), Genera of fishes, amphibians, turtles and phytosaurs are common to the Stubensandstein and the Huai Hin Lat Formation, This clearly suggests that in the Norian, dispersal of non-marine vertebrates was possible across Eurasia between Central Europe and the Indochina block of SE Asia, In- terestingly, no assemblages closely similar to Fig1 Map of SE Asia showing approximate limits between that from the Huai Hin Lat Formation are cur- the Shan-Thai and Indochina blocks, and the location of rently known from China (where, admittedly, fossiliferous areas or localities mentioned in text (in italics) Upper Triassic vertebrates are very poorly repre- sented; Sun, 1989), Possible dispersal routes across Late Triassic Eurasia are still poorly known, but they must have existed, hitherto found in the Nam Phong Formation consists of the fused distal ends of the ischia of a large prosauropod dinosaur (Buffetaut et al#, Upper Triassic: a prosauropod dinosaur from the 1995), A more accurate identification is not pos- Nam Phong Formation sible on the basis of the available material, As prosauropods had a nearly world-wide distribu- The Nam Phong Formation, which unconform- tion, on both Gondwana and Laurasia, in the ably overlies the Huai Hin Lat Formation, con- Late Triassic and Early Jurassic, the occurrence sists of sandstones and mudstones of mainly flu- of an indeterminate prosauropod on the vial origin, It has yielded very few fossils, and its Indochina block in the Rhaetian is not especially age has long remained uncertain, Racey et al# surprising or significant, Abundant prosauropod (1994, 1996) reported palynomorphs indicating remains, belonging to several taxa, have been an age no younger than Rhaetian and no older found in the Lower Lufeng Beds of Yunnan in than Ladinian, Since the underlying Huai Hin Lat southern China, but, after much controversy Formation is well dated as Norian, a Rhaetian over their age (for a recent review, see Dong, age is likely for the Nam Phong Formation, 1992), the Lower Lufeng Beds are now usually The only recognisable vertebrate element dated as Lower Jurassic (on the basis of paly- Mesozoic vertebrates from Thailand 85 Table 1 Main Mesozoic vertebrate-bearing formations of northeastern Thailand with their possible ages and significant fossils Khok Kruat Formation Aptian-Albian Thaiodus, Psittacosaurus, Iguanodontidae Phu Phan Formation Barremian? Theropod footprints Sao Khua Formation Valanginian-Hauterivian? Siamotyrannus, Phuwiangosaurus, Ornithomimosauria Phra Wihan Formation Berriasian? Theropod footprints Phu Kradung Formation Late Jurassic Temnospondyls, euhelopodid sauropods Nam Phong Formation Rhaetian Prosauropods Huai Hin Lat Formation Norian Lungfish, Cyclotosaurus, Proganochelys, phytosaurs nomorphs and molluscs), although their lower the Khorat Plateau, Among them are the first di- part is sometimes referred to the Rhaetian, In nosaur remains from the Jurassic of Thailand, this connection, it is worth mentioning that an which consist of isolated teeth of sauropods and especially large prosauropod from the lower theropods, The theropod teeth do not exhibit part of the Lower Lufeng Beds has been de- any particular features which could point to scribed as Jingshanosaurus xinwaensis by their biogeographical affinities, The sauropod Zhang and Yang (1994), who consider it to be teeth are broad and spoon-shaped, and com- Upper Triassic, Whether the apparently even pletely different from those referred to larger prosauropod from Thailand was more or Phuwiangosaurus, the most frequent sauropod less closely related to Jingshanosaurus is uncer- in the Lower Cretaceous Sao Khua Formation of tain on the basis of the available material, the Khorat Plateau (see below), They are more reminiscent of those of the euhelopodid dino- saurs from the Jurassic of China, such as Jurassic: vertebrates from the Phu Kradung Euhelopus (Wiman, 1929) or Mamenchisaurus Formation of the Khorat Plateau and similar (Russell and Zheng, 1993), Although the evi- formations of the Shan-Thai block dence is admittedly still slight, these teeth sug- gest that the Jurassic sauropods of SE Asia be- The Phu Kradung Formation of the Khorat Pla- longed to the same group as the Chinese ones, teau was once dated as Lower Jurassic, Because Other interesting vertebrate fossils from the all the overlying formations of the Khorat Group Phu Kradung Formation are vertebral elements are now considered as