Varavudh Suteethorn

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

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.KurzfassungDie Revision der Süßwasser-Haifauna von der Phu Kradung Formation in NO-Thailand führt zur Identifikation einer neuen Art von Acrodus, die den jüngsten Nachweis dieser Gattung darstellt und ihre Verdrängung in Süßwasser-Ökosystemen nach dem Toarc bestätigt. Die weitere Haifauna beinhaltet Zähne von Hybodus sp., aff. Hybodus sp., dermale Dentikel von Hybodontiden, Jiaodontus sp., Lonchiodon sp. A, Lonchiodon sp. B., Heteroptychodus cf. H. kokutensis und dorsale Flossenstachel. Das Vorkommen von Jiaodontus und von ungewöhnlichen hybodontiden dermalen Dentikeln deutet auf ein jurassisches Alter für den größten Teil der Phu Kradung Formation hin, während der Nachweis von Heteroptychodus ein unterkretazisches Alter für den obersten Teil der Formation andeutet. Allerdings bleibt das Alter der Phu Kradung Formation unsicher, da palynologische Daten, detritale Zirkone und die Wirbeltierpaläontologie widersprüchliche Resultate ergeben. Allerdings dürfte dies auf jeden Fall den ältesten Nachweis von Heteroptychodus darstellen und somit einen thailändischen Ursprung dieser Gattung andeuten, die Acrodus in den Süßwasser-Ökosystemen Thailands verdrängt haben mag. Zusammen mit Acrodus deutet das Vorkommen von Lonchiodon sp. A auf einen europäischen Einfluss auf die Haifauna der Phu Kradung Formation hin.

Late Palaeozoic and Mesozoic Continental Ecosystems in SE Asia

Non-marine Late Palaeozoic and Mesozoic formations are widespread in mainland SE Asia. Although the first reports on fossils from some of these formations were published as early as the 1890s, it is only since 1980 that floras and faunas from the Permian, Triassic, Jurassic and Cretaceous of SE Asia have received the attention they deserve. Fieldwork in various parts of Thailand and Laos has revealed a succession of fossil assemblages that now allows a reconstruction of the evolution of continental ecosystems in that part of the world during the Late Palaeozoic and the Mesozoic. The first papers in this book present the geological background of these floral and faunal successions, as well as historical aspects of their discovery. Descriptions of new taxa and review papers deal with plants, sharks, bony fishes, turtles, crocodilians, dinosaurs and mammal-like reptiles. Papers about the Mesozoic palaeobiogeography, environments and climates of Asia conclude the volume.

Evidence of Egg Diversity in Squamate Evolution from Cretaceous Anguimorph Embryos

Lizards are remarkable amongst amniotes, for they display a unique mosaic of reproduction modes ranging from egg-laying to live-bearing. Within this patchwork, geckoes are believed to represent the only group to ever have produced fully calcified rigid-shelled eggs, contrasting with the ubiquitous parchment shelled-eggs observed in other lineages. However, this hypothesis relies only on observations of modern taxa and fossilised gecko-like eggshells which have never been found in association with any embryonic or parental remains. We report here the first attested fossil eggs of lizards from the Early Cretaceous of Thailand, combining hard eggshells with exquisitely preserved embryos of anguimoph (e.g. Komodo dragons, mosasaurs). These fossils shed light on an apparently rare reproduction strategy of squamates, demonstrate that the evolution of rigid-shelled eggs are not an exclusive specialization of geckoes, and suggest a high plasticity in the reproductive organs mineralizing eggshells.

Strontium isotopes and the long-term residency of thalattosuchians in the freshwater environment

Abstract. Thalattosuchians are crocodylomorphs mainly known from marine strata of Early Jurassic to Early Cretaceous age. They represent the earliest crocodylomorph radiation to an aquatic habitat and their evolutionary history offers very few records from freshwater settings. Here, we report several exquisitely preserved thalattosuchian skulls attributed to a derived teleosaurid from a pedogenic horizon located at the base of a fluvial series of alternating silts and sandstones of the Phu Kradung Formation (Upper Jurassic) of northeastern Thailand. Using laser ablation multicollector inductively coupled mass spectrometry (MC-ICP-MS) on tooth enamel and dentine, we measured isotopic ratios of strontium (87Sr/86Sr) to test the habitat of these teleosaurids. In addition, Sr concentrations of the dental tissues were estimated from the calibrated signal intensities of the Sr isotope measurements. The dataset includes bioapatite (teeth or scales) of eight terrestrial and five aquatic vertebrates. Theropods exhibit lower Sr concentrations both in enamel and dentine compared to others groups, a pattern in accordance with the calcium biopurification process, which predicts that Sr concentrations in the body of vertebrates decrease up the trophic chain. It also excludes the possibility that diagenesis has completely overprinted the Sr isotope compositions of the fossil assemblage, which exhibits a homogeneous 87Sr/86Sr signature above the Late Jurassic seawater value. Values for teleosaurid teeth are in the range of other values for vertebrates in the continental assemblage and imply that these crocodylomorphs did not migrate between freshwater and marine habitats at least in the time constraint of the mineralizing tooth. This result represents the first demonstration that a population of teleosaurids was established for a prolonged time in a freshwater environment.Whether the ability of teleosaurids to inhabit freshwater habitats is a secondary adaptation or whether it is plesiomorphic and inherited from freshwater ancestors is discussed.

Early Cretaceous vertebrates from the Xinlong Formation of Guangxi (southern China): a review

The vertebrate assemblage from the Early Cretaceous non-marine Xinlong Formation of the Napai Basin, in the south-western part of Guangxi Zhuang Autonomous Region (southern China), is reviewed. The assemblage includes chondrichthyans (at least six species of hybodont sharks including Hybodus, Thaiodus, Heteroptychodus and Acrorhizodus ), actinopterygians (Halecomorphi and Ginglymodi), turtles (the adocid Shachemys and the carettochelyid Kizylkumemys ), crocodilians (cf. Theriosuchus ) and dinosaurs (the sauropods Fusuisaurus and Liubangosaurus , carcharodontosaurid and spinosaurid theropods, iguanodontians and a possible psittacosaurid). This assemblage shows many similarities to those from non-marine formations of the Khorat Group of north-eastern Thailand. It seems to be particularly close to that from the Khok Kruat Formation, considered as Aptian in age, as shown especially by sharks and turtles and by the presence of iguanodontians. An Aptian age is therefore proposed for the Xinlong Formation. A study of the stable oxygen and carbon isotope compositions of reptile apatite suggests that this part of South China experienced subtropical arid conditions during the deposition of the Xinlong Formation. In its composition, the vertebrate fauna from the Xinlong Formation seems to be more similar to coeval faunas from SE Asia than to assemblages from northern China (including the Jehol Biota). Although this may partly reflect different depositional and taphonomic environments (fluvial for the Xinlong Formation versus lacustrine for the Jehol Biota) it seems likely that, during Early Cretaceous time, southern China and SE Asia were part of a distinct zoogeographical province, different from that corresponding to northern China. This may be the result of both climatic differences (with relatively cool climates in northern China versus a subtropical climate in the south) and geographical barriers such as mountain chains.

PRELIMINARY INVESTIGATION OF SEASONAL PATTERNS RECORDED IN THE OXYGEN ISOTOPE COMPOSITIONS OF THEROPOD DINOSAUR TOOTH ENAMEL

Abstract Oxygen isotope compositions of tooth enamel increments in theropod dinosaurs are investigated as potential proxies of climate seasonality. Six teeth of large carnivorous theropods collected from four Cretaceous formations deposited under contrasted climates have been sampled. These teeth have been analyzed for the oxygen isotope compositions of their apatite phosphate (δ18Op) through incremental sampling performed along the major growth axis. Significant fluctuations in oxygen isotope compositions along the growth axis of each tooth are observed and interpreted as reflecting seasonality in ingested local surface water δ18Ow values. Fluctuations in δ18Op values of theropod teeth from the Aptian of Thailand and Cenomanian of Morocco vary similarly to meteoric water δ18Omw values occurring today in sub-tropical regions subjected to large seasonal amounts of precipitations. A dinosaur tooth recovered from the more inland and mid-latitude Nemegt Formation of Mongolia shows a seasonal pattern similar to present-day cold temperate and continental climate. Finally, the high latitude and coastal Kakanaut Formation (Russia) experienced strongly dampened seasonal variations, most likely due to the influence of warm Pacific oceanic currents. Such conditions occur today in high latitude regions submitted to marine influence. These results further highlight the potential of using the oxygen isotope compositions of large theropod teeth to reconstruct past seasonal variations of terrestrial climates. Increased knowledge of past seasonality may help to better understand the complex interactions between climate and the dynamics of land biodiversity in terms of ecological adaptations, biogeography and the evolutionary history of organisms.

A new primitive eucryptodiran turtle from the Upper Jurassic Phu Kradung Formation of the Khorat Plateau, NE Thailand

A new genus and new species of primitive eucryptodiran turtle, Phunoichelys thirakhupti gen. et sp. nov., is described on the basis of shell remains from the lower part of the Phu Kradung Formation, at Phu Noi locality, Kalasin Province, NE Thailand. It is assigned to Xinjiangchelyidae on the basis of the marginals covering the lateral end of the costals and the anal scutes invading the hypoplastra. The new taxon is further characterized by a low and rounded carapace without a cervical notch; the whole carapace and plastron covered with a clear ornamentation consisting of tiny irregular vermiculated furrows; a complete neural series that reaches the suprapygal; a very wide and short cervical scute; relatively wide vertebral scutes; and a long first thoracic rib that extends along the full width of the first costal. The sutured plastron/carapace connection and the marginals covering the lateral end of the second to seventh costals suggest that the turtles from Phu Noi may be related to some primitive xinjiangchelyids from the Sichuan Basin. The discovery of a xinjiangchelyid turtle in the lower part of the Phu Kradung Formation supports a Late Jurassic age for that part of the formation.

New Evidence of Sauropod Dinosaurs from the Early Jurassic Period of Thailand

The oldest dinosaur assemblages of Thailand deposit in continental sedimentary rocks of the Nam Phong Formation. Not only Isanosaurus attavipatchi was discovered but at least two more species of basal sauropods were found. A partial skeleton from Phu Hin Tan locality refers to sauropod taxon A. It is different from Isanosaurus and shares some characteristics with basal sauropods in the Early Jurassic. The sauropod taxon B was found in Non Sra Ard locality. Base on postcranial skeleton, sauropod taxon B shares some characteristics of the family Vulcanodontidae. Moreover, several fragments of the sauropods specimen are also found in Pha Khok Wang Yang and Phu Noi localities. All of the evidences above indicate that there are a highly diversity of sauropods in the Nam Phong Formation. At least three sauropod species (including Isanosaurus) were found in the Nam Phong formation. The issue about the age of the Nam Phong has been debated for a long time between the Triassic and Jurassic age. All of sauropodomorphs, in this study, are more likely the Early Jurassic period dinosaurs than the Triassic period dinosaurs. And they have deposited in the upper part of Nam Phong Formation.

A new species of Cuora (Testudines: Geoemydidae) from the Miocene of Thailand and its evolutionary significance

A new species of Cuora , Cuora chiangmuanensis sp. nov., is described on the basis of a nearly complete shell with limb bones from the late Middle – early Late Miocene Chiang Muan Mine, Phayao Province (Northern Thailand). C. chiangmuanensis is distinguished from other fossil and living Cuora species mainly on the basis of its plastral morphology. Among fossil and extant Cuora taxa, the new species appears to be a missing link between the taxa from Southeast Asia and those from East Asia. It represents the earliest record of the genus and demonstrates that by 11–12 Ma, Asian box turtles were already present in Southeast Asia.