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A carcharodontosaurid theropod (Dinosauria, Saurischia) in the Sao Khua Formation (Early Cretaceous, Barremian) of Thailand
... nine theropods have been reported from the Khorat Group of northeastern Thailand. Until now, five theropods have been found from the Sao Khua Formation (e.g., Buffetaut and Suteethorn 2012; see the geological setting part in this paper). There are at least two new coelurosaurian theropod specimens from the Sao Khua Formation that may belong to the Megaraptora. ...
... Until now, five distinct theropods have been reported from the Sao Khua Formation. Theses consists of a possible compsognathid (Buffetaut and Ingavat 1984), teeth of the spinosaurid Siamosaurus suteethorni (Buffetaut and Ingavat 1986), the theropod Siamotyrannus isanensis (Buffetaut et al. 1996), the ornithomimosaur Kinnareemimus khonkaenensis ), and the partial skull of a carcharodontosaurid (Buffetaut and Suteethorn 2012). ...
Megaraptora is a clade of mid to large-sized theropods that are long-snouted, large-clawed, highly pneumatized, and have long and gracile metatarsals. The basal member was reported from the Barremian of Japan. A more derived clade, the Megaraptoridae, is known from the Cenomanian to Santonian of Gondwana. Here two new basal coelurosaurs from the Lower Cretaceous Sao Khua Formation of Thailand are described and named as Phuwiangvenator yaemniyomi gen. et sp. nov. and Vayuraptor nongbualamphuensis gen. et sp. nov. Phuwiangvenator is a megaraptoran coelurosaur and diagnosed by the ventrally flat sacral vertebrae with sulci in the anterior and posterior region of the centra and the anterior rim of metatarsal IV sloping proximolaterally to distomedially and being much lower than that of metatarsal III anteriorly. Vayuraptor is a basal coelurosaur and diagnosed by its astragalus which has two horizontal grooves, two fossae at the base of the ascending process, the ascending process being straight laterally and straight and parallel medially with the medial rim sloping to the tip laterally, and a long and slender astragalar ascending process. Although the position of the basal coelurosaur Vayuraptor remains unclear and must await further discovery, megaraptoran affinities are likely. The Early Cretaceous megaraptoran fossil record has been recovered from the Barremian to Aptian of Asia. All Asian megaraptorans might be a monophyletic clade or a paraphyletic series relative to the Megaraptoridae. Several specimens have been reported from the Aptian to mid-Cretaceous of Australia, and one report from the Albian of South America. These fossils show a high diversity of the Early Cretaceous megaraptorans and a wide distribution during that time. The clade then became more provincial in the Late Cretaceous.
... Currently, the Sao Khua dinosaur assemblage is heavily dominated by a rich array of at least seven tetanuran non-avian theropods including the?metriacanthosaur Siamotyrannus (Buffetaut et al., 1996), spinosaurid "Siamosaurus" (Buffetaut and Ingavat, 1986;Amiot et al., 2009), a possible second spinosaurid taxon "Phu Wiang spinosaurid B" ( [Samathi et al., 2021]), megaraptoran Phuwiangvenator (Samathi et al., 2019a), and coelurosaurian Vayuraptor (Samathi et al., 2019a(Samathi et al., , 2019b, ornithomimid Kinnareemimus , an unnamed carcharodontosaurid from Phu Wang (Buffetaut and Suteethorn, 2012), and an indet. Tetanuran (Buffetaut and Ingavat, 1984, formerly considered a compsognathid, see Samathi et al., 2019b), and at least two sauropods, including the somphospondylan Phuwiangosaurus (Martin et al., 1994), and an unnamed taxon (Buffetaut and Suteethorn, 1999). ...
We describe the sedimentology, geochronology, and geochemistry of the Early Cretaceus Sao Khua Formation of the Khorat Basin, northeastern Thailand, and report a temporal range adjustment for its dinosaurian assemblage. Facies analysis and architectural studies reveal that sedimentation occurred within a floodplain setting fed by large meandering bedload-rich channels. Interfluve areas comprised freshwater lakes and emergent areas subject to pedogenic modification. Multiple paleosol types are identified and geochemistry is indicative of a stable humid subtropical climate regime. Based on radiometric dating of detrital zircons (via LA-ICP-MS), we interpret that the middle part of the Sao Khua Formation was deposited no later than 133.8 (±1.8) Ma (late Valanginian), and grain ages collected from the overlying lowermost Phu Phan Fm constrain sedimentation of the upper part of the Sao Khua Formation to no earlier than 132.4 (±2.0) Ma (early Hauterivian). In consideration of the Early Cretaceous regional tectonic framework, we interpret that youthful igneous zircon grains are derived from the adjacent South China-Vietnam South Borneo Volcanic Arc. We establish that the entombed dinosaur biota (including members of the Ornithomimosauria, Spinosauridae, Megaraptora, and Somphospondylia) is ~5–9 million years older than previously recognized and that these records are among the oldest known globally for these clades. Constraining the age of the Sao Khua Formation indicates that the shift from sauropod-dominated, ornithischian depauperate ecosystems of the Sao Khua Formation to iguanodontian-rich ecosystems of the Khok Kruat Formation occurred sometime between the early Hauterivian and Aptian on the Khorat Plateau.
... Phu Wiang District, Khon Kaen Province Description: A large-bodied carcharodontosaurid with completely fused interdental plates resembling Carcharodontosaurus, Mapusaurus, and Shaochilong. It differs from Sinraptor and Tyrannosaurus in which the interdental plates are separated and differs from Allosaurus where the individual plates can be distinguished although there is some level of fusion (all information from Buffetaut and Suteethorn, 2012). ...
Several non-avian theropod dinosaurs, as well as some Mesozoic birds, have been reported from Southeast Asia. The fossils are dominantly found in northeastern Thailand, however, one bizarre theropod has been described from Laos, one theropod has been reported from Malaysia, and some avian and non-avian theropods have been recently reported from Myanmar. The temporal distribution of Southeast Asian theropods ranges from the Late Jurassic to the mid-Cretaceous. All non-avian theropod faunas from Southeast Asia consist of non-maniraptoran tetanurans. They show similarity to Chinese plus Japanese theropods during the Early Cretaceous in broad systematic terms. During this time, megaraptorans can be found only in Japan, Australia, Brazil, and possibly Thailand, whereas tyrannosauroids can be found in China, Europe, possibly Brazil and Australia. Spinosaurids, carcharodontosaurians, and some coelurosaurs such as ornithomimosaurs were almost cosmopolitan. Metriacanthosaurids, on the other hand, were endemic to Europe and Asia including China and Thailand during the Middle to Late Jurassic.
... Contrasting with this rich and relatively continuous fossil record of Carcharodontosauridae starting with the Aptian, the first half of its evolutionary history is very poorly documented (Fig. 5B). Prior to the identification of UAIC (SCM1) 615, only two occurrences of pre-Aptian Cretaceous carcharodontosaurids were reported, one from the Barremian of Spain (Ortega et al., 2010;Gasca et al., 2014) and the other from the Barremian of Thailand (Buffetaut and Suteethorn, 2012). The Early Cretaceous Kelmayisaurus from Xinjiang, western China, was recognized as a carcharodontosaurid of possibly ?Valanginian to Aptian in age by Brusatte et al. (2012), but the deposits yielding these remains (the Lianmugin, or Lianmuxin, Formation of the Tugulu Group) were dated as AptianeAlbian by Eberth et al. (2001;see also Tong et al., 2009). ...
... As described in Section 3, however, several vertebrate groups from the Xinlong Formation show interesting similarities to those from the Khok Kruat Formation. These resemblances can be summarized as follows: (Buffetaut & Ingavat, 1986;Buffetaut & Suteethorn, 2012) as well as from the Khok Kruat Formation Azuma et al. 2011). However, a significant difference between the dinosaur faunas from these formations is that ornithischian dinosaurs have never been reported from the Sao Khua Formation, while they are represented in the Khok Kruat Formation by both psittacosaurids (Buffetaut & Suteethorn, 1992;Buffetaut, Suteethorn & Khansubha, 2007) and hadrosauroid ornithopods . ...
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.
Phuwiangvenator yaemniyomi is a mid-sized, early branching megaraptoran theropod from the Lower Cretaceous Sao Khua Formation of Phu Wiang Mountain, Khon Kaen Province, northeastern Thailand. The holotype includes dorsal and sacral vertebrae, lower legs, hand and foot elements. Here we describe new skeletal material pertaining to the same individual representing the holotype of Phuwiangvenator based on size, shape, and shared phylogenetic affinities. This material was recovered at the same quarry as the holotype and consists of an incomplete fibula, left and right metatarsals. A new autapomorphy observed from the new material is the presence of a long, deep fossa between the lateral and medial distal condyles of the metatarsal II that extends to the distal articular facet is visible in anterior view. The metatarsal III of Phuwiangvenator is relatively short, more similar to the proportion present in basal carcharodontosaur Concavenator than in the derived megaraptorans, but more gracile than other basal allosauroids. Its hindlimb proportions are similar to the basal carcharodontosaur Neovenator than other more derived megaraptorans and coelurosaurs. Phuwiangvenator shows a combination of features shared with allosauroids and basal coelurosaurs and appears to be “intermediate” between non-megaraptorid and megaraptorid theropods. The present work adds anatomical data on this theropod and provides information on the early evolution of the Megaraptora.
The isolated fossil remains of an allosauroid theropod from the Lower Cretaceous Khok Kruat Formation of Khorat, Thailand, are described in this study. Detailed observations support the establishment of a new allosauroid, Siamraptor suwati gen. et sp. nov. This new taxon is based on a composite cranial and postcranial skeleton comprising premaxilla, maxilla, jugal, surangular, prearticular, articular, vertebrae, manual ungual, ischium, tibia, and pedal phalanx. It is distinguished from other allosauroids by characters such as a jugal with straight ventral margin and dorsoventrally deep anterior process below the orbit, a surangular with a deep oval concavity at the posterior end of the lateral shelf and four posterior surangular foramina, a long and narrow groove along the suture between the surangular and the prearticular, an articular with a foramen at the notch of the suture with the prearticular, an anterior cervical vertebra with a pneumatic foramen (so-called ‘pleurocoel’) excavating parapophysis, and cervical and posterior dorsal vertebrae penetrated by a pair of small foramina bilaterally at the base of the neural spine. The presence of a huge number of camerae and pneumatopores in cranial and axial elements reveals a remarkable skeletal pneumatic system in this new taxon. Moreover, the phylogenetic analyses revealed that Siamraptor is a basal taxon of Carcharodontosauria, involving a new sight of the paleobiogeographical context of this group. Siamraptor is the best preserved carcharodontosaurian theropod in Southeast Asia, and it sheds new light on the early evolutionary history of Carcharodontosauria.
A fragmentary fossil found in the Barremian Sao Khua Formation of northeastern Thailand seems to fit the apical part of a sclerorhynchid rostral tooth. However, it appears different from all other known sclerorhynchid rostral teeth, and would likely represent a new genus, one of the oldest known. Despite intensive research conducted in the Sao Khua Formation the past 10 years, no other sclerorhynchid remains were recovered. This fossil remains therefore quite mysterious, and its identification tentative at best.
A new large-bodied theropod dinosaur, Datanglong guangxiensis gen. et sp. nov., was recovered from the Lower Cretaceous Xinlong Formation of the Datang Basin, Guangxi. It is unique in several features including: posteriormost dorsal vertebra with teardrop-shaped pneumatic foramen confined by enlarged pcdl, acpl and the centrum; posteriormost dorsal with well-developed, horizontal prpl; posteriormost dorsal with a parapophysis projecting more laterally than the diapophysis; brevis fossa shallow with short, ridge-like medial blade; and iliac pubic peduncle with posteroventrally expanded margin. Cladistic analysis supports the idea that this new taxon Datanglong guangxiensis is a primitive member of the Carcharodontosauria in possessing two unambiguous synapomorphies: large external pneumatic foramina and internal spaces present in the lateral surface of ilium, and a peg-and-socket ischiac articulation with the ilium. The presence of the new taxon from Guangxi further confirms that Carcharodontosauria were cosmopolitan large-bodied predators during the Early-mid Cretaceous.
A nearly complete right maxillary or left dentary tooth (NHMG 10858) from the Lower Cretaceous Xinlong Formation of the Napai Basin, Fusui County, Guangxi, southern China, is described. The tooth is large in size, with a CBL of 37 mm. Given the geological age and its crown morphology, including the size, it is most likely that the tooth belongs to a carcharodontosaurid. The recovered specimen represents one of the largest theropod teeth hitherto reported from the Early Cretaceous of Asia.
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