The Mamenchisaurids were a group of non-Neosauropod Sauropods (i.e. outside the largest grouping of Sauropods) which formed a significant part of the fauna of East Asia during the Middle and Late Jurassic. They can be distinguished by highly pneumatised and elongated cervical vertebrae, as well as procoelous vertebrae on the front part of the caudal spine (procoelous vertebrae have a convex forward disk and a concave rear disk), which were distinctive during the Jurassic, but evolved convergently in several Neosauropod groups during the Cretaceous.
Most known Mamenchisaurids come from China, and for a long time they were thought to be restricted to that country. However, in 2005 fragmentary remains attributed to the group were recovered from the Middle to Late Jurassic Khlong Min Formation of Krabi Province in southern Thailand. In 2013, further fragmentary remains were found in the Late Jurassic to Early Cretaceous Phu Kradung Formation of northeastern Thailand, and in 2019 a new species of Mamenchisaurid, Wamweracaudia keranjei, was described on the basis of a partial skeleton from the Late Jurassic Tendaguru Formation of southeastern Tanzania, establishing the presence of the group in Africa.
In a paper published in the journal Scientific Reports on 8 July 2026, Apirut Nilpanapan of the Department of Biology at Mahasarakham University, Sita Manitkoon of the Palaeontological Research and Education Centre and Vertebrate Palaeontology and Evolution Research Unit at Mahasarakham University, Varavudh Suteethorn of the Khon Kaen Geopark Association, and Komsorn Lauprasert also of the Department of Biology and Evolution Research Unit at Mahasarakham University, describe a new species of Mamenchisaurid Sauropod from the Phu Kradung Formation of northeastern Thailand.
The new species is named on the basis of material collected from the Phu Noi Locality, which is in the village of Ban Din Chi in the Kham Muang District of Kalasin Province, in the northeast of Thailand. Here an outcrop of the Phu Kradung Formation has produced one of the most diverse non-marine Vertebrate fossil assemblages in Southeast Asia. The Phu Kradung Formation comprises a series of sandstones, siltstones, and mudstones laid down in a fluvial environment, within a continental basin.
The precise age of the Phu Kradung Formation is unknown, as it lacks any radiometrically datable horizons. However, regional stratigraphic correlations, Vertebrate assemblages, and detrital zircon data suggest that it is of Late Cretaceous origin, possibly with the uppermost part of the formation extending into the earliest Cretaceous.
The Phu Noi outcrop comprises numerous channel horizons formed within a braided river, rather than horizontal layers extending across the whole site. It has three fossil-bearing horizons. The lowest of these is a grey conglomeratic sandstone laid down in a channel bottom. About 10 m above this, the middle horizon is a brownish-purple and greenish-grey sandy siltstone and mudstone. At the same level as this, but about 400 m to the southwest, the upper horizon is a greyish siltstones within proximal floodplain deposit.
The specimen from which Nilpanpan et al. describe the new species comes from the middle horizon, which is particularly rich in Vertebrate remains, having previously yielded Hybodont Sharks, Ginglymodian Fish, Lungfish, Eucryptodiran Turtles, Teleosaurid Crocodyliformes, and Neornithischian Dinosaurs, and with Brachyopid Temnospondyl, Rhamphorynchoidea Pterosaur, Tyrannosauroid and Metriacanthosaurid Theropod specimens currently being studied. This faunal assemblage shows a strong affinity to the Late Jurassic and earliest Cretaceous faunas of the Junggar, Turpan, and Sichuan basins of China.
The new species is named Uragasaurus kalasinensis, where 'Uragasaurus' derives from 'Uraga' (उरग) the Sanskrit word for Snake, in reference to the long, serpentine, neck of Sauropod Dinosaurs, plus '-saurus' (σαύρος), the Greek for Lizard, a common suffix in Dinosaur names, and 'kalasinensis' means 'from Kalasin' in reference to the province where the specimen was discovered.
Uragasaurus kalasinensis is described from a single isolated anterior dorsal vertebra (PRC 460), from the Phu Noi locality, which is housed in the collection of the Palaeontological Research and Education Centre at Mahasarakham University. A number of other Sauropod elements were found close to this specimen in the same level, which Nilpanpan et al. refer to Uragasaurus kalasinensis. However, because these elements cannot be assigned to the same original Animal with 100% confidence, and they do not have overlapping diagnostic features, they are not included in the formal description of the species. This material includes two anterior dorsal neural arches (KS 34-581 & KS 34-586), a left coracoid (KS 34-587), a left fibula (KS 34-588), a middle cervical vertebra (KS 34-602a), a right cervical rib (KS 34-602b), a middle-to-posterior dorsal vertebra (KS 34-692), and a posterior dorsal vertebra (PN 13-23).
The anterior dorsal vertebra assigned to Uragasaurus kalasinensis has a prominent, elongated teardrop-shaped pneumatic fossae on the distal portion of the transverse processes, intraprezygapophyseal laminae meeting ventromedially to form a Y-shaped configuration in anterior view, incorporating a single vertical intraprezygapophyseal lamina, and a shallow, subtriangular pleurocoel lacking an internal septum.
A computed tomography of specimen PRC 460 showed that its centrum has a camellate internal pneumatic structure composed of numerous small, irregular chambers separated by thin bony septa, although it was not possible to accurately measure the dimensions of these cavities due to mineral infilling. This is a structure unique to advanced Mamenchisaurids, which differs from the procamerate internal structure seen in certain Neosauropods and the camerate condition found in Macronarians and Diplodocoids.
Phylogenetic analysis of the taxonomic affinities of Uragasaurus kalasinensis consistently recovered the species as a basal Mamenchisaurid, although its precise placement within this group was hard to determine, which is unsurprising given the limited nature of the material. However, the same analysis consistently found Rhomaleopakhus turpanensis, a species formerly classified as being a member of the Mamenchisauridae, as being outside the group, which Nilpanpan et al. suggest may indicate the need to re-evaluate the taxonomic status of a number of Late Jurassic Asian Sauropods.
A previous Mamenchisaurid specimen, KS26-4, was described from the Phu Dan Ma locality in 2013. This specimen comprises a nearly complete posterior cervical vertebra and two fragmentary ribs. Since this material did not contain any elements considered reliably diagnostic within the Mamenchisauridae, it was not formally described as a new species. This lack of diagnostic features, combined with a lack of shared elements with the material assigned to Uragasaurus kalasinensis leads Nilpanpan et al. to refrain from assessing whether it belongs to the same species.
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