First occurrence of brachyopid temnospondyls in Southeast Asia and review of the Mesozoic amphibians from Thailand

The non-marine Mesozoic sedimentary rocks of Thailand,which consist of the Indochina block and the Sibumasu block, have yieldedseveral terrestrial and aquatic vertebrate fossils, but only few amphibianremains have been reported. Here, we present an overview on the Thaiamphibian palaeo-diversity based on the literature, re-examination ofpublished material, new findings, and unpublished material. Thai amphibianfossil remains are assigned to Stereospondyli (Cyclotosauridae,Plagiosauridae, and Brachyopoidea) and Anura and were discovered from fourformations, ranging from the Upper Triassic to Lower Cretaceous of Thailand.The occurrence of Brachyopidae in Thailand, which are related to Chineseforms, supports the previous hypothesis of physical connections between theIndochina blocks and the Sibumasu block during the Mesozoic era

Ornithischian dinosaurs in Southeast Asia: a review with palaeobiogeographic implications

Ornithischian dinosaurs have been discovered in Thailand, Laos, and Malaysia. These bird-hipped herbivores remain relatively rare by comparison with saurischian dinosaurs. In the Late Jurassic, stegosaurs and basal neornithischians from Thailand showed similarities to Middle-Late Jurassic taxa from China. Ornithischians appeared in the fossil record again during the late Early Cretaceous (Aptian-Albian) of Thailand and Laos. They are represented by non-hadrosaurid iguanodontians and basal ceratopsians. A few specimens have been reported from poorly dated Early Cretaceous rocks of Malaysia. Here, we illustrate the diversity of ornithischian assemblages in Southeast Asia and discuss their palaeobiogeographical implications

Ornithischian dinosaurs in Southeast Asia: a review with palaeobiogeographic implications

Ornithischian dinosaurs have been discovered in Thailand, Laos, and Malaysia. These bird-hipped herbivores remain relatively rare by comparison with saurischian dinosaurs. In the Late Jurassic, stegosaurs and basal neornithischians from Thailand showed similarities to Middle-Late Jurassic taxa from China. Ornithischians appeared in the fossil record again during the late Early Cretaceous (Aptian-Albian) of Thailand and Laos. They are represented by non-hadrosaurid iguanodontians and basal ceratopsians. A few specimens have been reported from poorly dated Early Cretaceous rocks of Malaysia. Here, we illustrate the diversity of ornithischian assemblages in Southeast Asia and discuss their palaeobiogeographical implications

Paleoneuroanatomy of an atoposaurid (Neosuchia, Crocodylomorpha) from the Sao Khua Formation (Thailand) and paleobiological implications

International audienceThe internal endocranial structures of an undescribed atoposaurid crocodylomorph from the Sao Khua Formation (Cretaceous: Berriasian-Barremian) in the North-East of Thailand are investigated. The specimen is comparable in size and external morphology to Theriosuchus grandinaris Lauprasert et al. 2011 but is preserved with the braincase uncrushed, contrary to the previously described holotype. We document for the first time the internal braincase structures in atoposaurids using synchrotron X-ray micro-computed tomography. The endocast of the braincase, associated nerves and arteries, auditory labyrinth, and cranial pneumatization, although quite deformed, are reconstructed at high resolution and compared to those of extant and fossil crocodylomorphs, representative of different ecological adaptations. This atoposaurid specimen shows an antero-posterior brain curvature and pericerebral spines (new structures), somewhat developed cerebral hemispheres, expanded semicircular canals with a more developed anterior one but an almost straight lateral one, a dorsoventrally expanded pituitary fossa, but also overdeveloped intertympanic diverticula and pharyngotympanic sinuses. The ecologicalsignificance of these structures is explored and, using different proxies and comparisons with extant taxa, we suggest that this specimen likely exhibited a downwardly tilted head posture (by about 10◦) and was sensitive to both low and mid frequencies. Functional comparisons are proposed between this specimen, extinct terrestrial crocodylomorphs (sebecosuchians), extant semi-aquatic crocodilians and aquatic (thalattosuchians) forms. From the morphology of the auditory labyrinth, we infer an enhanced sensitivity to pitching rather than yawing. Several hypotheses are formulated regarding the pneumatization of the skull. These features are discussed in ecological and phylogenetic frameworks. Our results highlight the need to gather new data, especially on altirostral forms, in order to deepen our understanding of the evolution of endocranial structures in crocodylomorphs with different ecological specializations, as well as to integrate them into new phylogenetic approaches

Fossil assemblage from the Khok Pha Suam locality of northeastern, Thailand: an overview of vertebrate diversity from the Early Cretaceous Khok Kruat Formation (Aptian-Albian)

The Khok Pha Suam locality in the province of Ubon Ratchathani, northeastern, Thailand, is known as “the last home of Thai dinosaurs”, because it belongs to the Lower Cretaceous Khok Kruat Formation (Aptian-Albian) which is currently the youngest Mesozoic vertebrate fossil producing formation in the Khorat Group. Here, we describe a diverse vertebrate assemblage, including hybodonts, ray-finned fishes, turtles, crocodyliforms, pterosaurs, and dinosaurs from the Khok Pha Suam locality. The updated data on the Khok Kruat fauna provides a better understanding of the variety and distribution of Early Cretaceous continental ecosystems, which are useful for palaeoenvironmental reconstruction. In addition to consolidating unincorporated data on fauna, this study also provides the palaeontological data necessary to illustrate the palaeoecosystem to the general public, as well as improving the academic value of the Pha Chan-Sam Phan Bok Geopark

Paleoneuroanatomy of an atoposaurid (Neosuchia, Crocodylomorpha) from the Sao Khua Formation (Thailand) and paleobiological implications

International audienceThe internal endocranial structures of an undescribed atoposaurid crocodylomorph from the Sao Khua Formation (Cretaceous: Berriasian-Barremian) in the North-East of Thailand are investigated. The specimen is comparable in size and external morphology to Theriosuchus grandinaris Lauprasert et al. 2011 but is preserved with the braincase uncrushed, contrary to the previously described holotype. We document for the first time the internal braincase structures in atoposaurids using synchrotron X-ray micro-computed tomography. The endocast of the braincase, associated nerves and arteries, auditory labyrinth, and cranial pneumatization, although quite deformed, are reconstructed at high resolution and compared to those of extant and fossil crocodylomorphs, representative of different ecological adaptations. This atoposaurid specimen shows an antero-posterior brain curvature and pericerebral spines (new structures), somewhat developed cerebral hemispheres, expanded semicircular canals with a more developed anterior one but an almost straight lateral one, a dorsoventrally expanded pituitary fossa, but also overdeveloped intertympanic diverticula and pharyngotympanic sinuses. The ecologicalsignificance of these structures is explored and, using different proxies and comparisons with extant taxa, we suggest that this specimen likely exhibited a downwardly tilted head posture (by about 10◦) and was sensitive to both low and mid frequencies. Functional comparisons are proposed between this specimen, extinct terrestrial crocodylomorphs (sebecosuchians), extant semi-aquatic crocodilians and aquatic (thalattosuchians) forms. From the morphology of the auditory labyrinth, we infer an enhanced sensitivity to pitching rather than yawing. Several hypotheses are formulated regarding the pneumatization of the skull. These features are discussed in ecological and phylogenetic frameworks. Our results highlight the need to gather new data, especially on altirostral forms, in order to deepen our understanding of the evolution of endocranial structures in crocodylomorphs with different ecological specializations, as well as to integrate them into new phylogenetic approaches

Fossil assemblage from the Khok Pha Suam locality of northeastern, Thailand: an overview of vertebrate diversity from the Early Cretaceous Khok Kruat Formation (Aptian-Albian)

The Khok Pha Suam locality in the province of Ubon Ratchathani, northeastern, Thailand, is known as “the last home of Thai dinosaurs”, because it belongs to the Lower Cretaceous Khok Kruat Formation (Aptian-Albian) which is currently the youngest Mesozoic vertebrate fossil producing formation in the Khorat Group. Here, we describe a diverse vertebrate assemblage, including hybodonts, ray-finned fishes, turtles, crocodyliforms, pterosaurs, and dinosaurs from the Khok Pha Suam locality. The updated data on the Khok Kruat fauna provides a better understanding of the variety and distribution of Early Cretaceous continental ecosystems, which are useful for palaeoenvironmental reconstruction. In addition to consolidating unincorporated data on fauna, this study also provides the palaeontological data necessary to illustrate the palaeoecosystem to the general public, as well as improving the academic value of the Pha Chan-Sam Phan Bok Geopark

New Cretaceous neosuchians (Crocodylomorpha) from Thailand bridge the evolutionary history of atoposaurids and paralligatorids

International audienceThe origin of modern crocodylians is rooted in the Cretaceous, but their evolutionary history is obscure because the relationships of outgroups and transitional forms are poorly resolved. Here, we describe a new form, Varanosuchus sakonnakhonensis gen. nov., sp. nov., from the Early Cretaceous of Thailand that fills an evolutionary gap between Paralligatoridae and Atoposauridae, two derived neosuchian lineages with previously unsettled phylogenetic relationships. Three individuals, including a complete skull and associated postcranial remains, allow for a detailed description and phylogenetic analysis. The new taxon is distinguished from all other crocodylomorphs by an association of features, including a narrow altirostral morphology, a dorsal part of the postorbital with an anterolaterally facing edge, a depression on the posterolateral surface of the maxilla, and fully pterygoid-bound choanae. A phylogenetic analysis confirms the monophyly and taxonomic content of Atoposauridae and Paralligatoridae, and we underline the difficulty in reaching a robust definition of Eusuchia. Furthermore, we put forward further arguments related to the putative terrestrial ecology with semi-aquatic affinities of atoposaurids based on their altirostral snout morphology and osteoderm ornamentation