Phuwiangvenator () is an extinct genus of megaraptoran theropod that lived during the Early Cretaceous period in what is now Thailand. It contains only the type species, P. yaemniyomi. The generic name of Phuwiangvenator comes from the Phu Wiang mountains, where the holotype was discovered, and the Latin word "venator" meaning hunter. The specific name, "yaemniyomi", is in honor of Sudham Yaemniyom, who was a historical paleontologist from Thailand and the first person to discover fossils there.
Discovery
The holotype specimen of Phuwiangvenator, designated SM-PW9B, is a partially-complete skeleton consisting of a dorsal vertebra, three sacral vertebrae, a right metacarpal, right manual phalanges and unguals, both tibiae, the left astragalocalcaneum, several left metatarsals, and several right pedal phalanges and unguals. It was discovered in 1993 by a team led by Preecha Sainongkham in the Sao Khua Formation of Khon Kaen province in Thailand. At the time of this discovery, Sainongkham was working at the Phu Wiang Dinosaur Museum. The specimen was transported to the Sirindhorn Museum in the town of Non Buri, which is near the locality where the fossils were discovered. The fossils were prepared and remained in the museum's collection until 2019 when Adun Samathi, Phornphen Chanthasit, and P. Martin Sander published a formal description, which was accompanied by a description of the closely related taxon, Vayuraptor. A few years after the description of the holotype, another specimen was discovered in the collections at the Sirindhorn Museum. This was described in 2022 by Adun Samathi (one of the original describers), Suravech Suteethorn, Nakorn Pradit, and Varavudh Suteethorn, the latter of whom was part of the original team which uncovered the holotype. They concluded, based on the reported type locality from which the specimen was retrieved as well as several characteristics of the bones themselves, that these bones likely belonged to the same individual animal as the holotype specimen. These additional elements were named as the topotype and were given the designation SM-PW9A. This specimen included both ends of the left fibula, several of the left metatarsals, and the distal ends of the right metatarsals. One of the metatarsals was later discovered to contain a fracture, which was studied and published on in 2023. The discovery of Phuwiangvenator in Thailand is used by its describers to suggest an Asian origin of megaraptora. They state that the existence of Vayuraptor in Thailand and Fukuiraptor in Japan are also evidence of this.
Description The authors of its original description estimate that Phuwiangvenator was probably about 6 metres (20 ft) long in life. From what is known of the skeleton, it likely had proportions similar to the related taxon Australovenator, which is known from slightly more complete remains. The authors name two autapomorphies for Phuwiangvenator. The first of these are short furrows on the ventral side of the sacral vertebrae on the front and rear ends. The other autapomorphy is a sloping rim of the fourth metatarsal which is angled away from the middle of the body at the dorsal end. This sloping fourth metatarsal is additionally unique in having the lowest corner relative to the third metatarsal of any known theropod.
Vertebrae Phuwiangvenator is only known from four vertebrae, one from the dorsal area and three from the sacrum. These vertebrae, as a whole, share numerous affinities with other large theropods. The dorsal vertebra is hourglass-shaped when viewed from above (or below), which is similar to the vertebrae of Fukuiraptor, Aerosteon, and numerous other avetheropods. In particular, the centrum of the only preserved dorsal vertebra does not have a pleurocoel or any lateral ridges, which resembles the condition observed in Gualicho, a theropod of controversial affinities. The three sacral vertebrae which are preserved are all fused and were damaged significantly during fossilization. However, the centra are well-preserved enough to show one of the key autapomorphies of the genus, the saci (or furrows) on the anterior and posterior portion of the bone.
Hands Most of the preserved finger bones have deep and well-defined attachment sites for ligaments, which resemble those found in the theropods Kileskus and Australovenator.
Legs The leg bones share numerous marked similarities with other megaraptorans. The tibia is more than twelve times longer than its mid-length anteroposterior width, which is a synapomorphy of megaraptorans and other coelurosaurs. There are also several characteristics of the astragalus and the metatarsals which resemble those of Australovenator. There is one major exception to the megaraptoran affinities of the holotype's leg bones; the anterolateral process of the lateral condyle is sharply curved downward, which is a condition seen in Neovenator and numerous tyrannosaurids. This led the authors of the paper to suggest that this trait, and other characteristics of the leg bones may be more widespread among theropods than was previously thought. In their subsequent analysis of the topotype material, Samathi and colleagues draw comparisons between the metatarsals of Phuwiangvenator with those of numerous theropods including Allosaurus, Concavenator, Neovenator, and Suchomimus. They use this to suggest that the condition seen in the species represents the ancestral condition of all avetheropods, rather than the derived condition seen in megaraptorids.
Classification
Phylogeny Samathi and colleagues performed a phylogenetic analysis in their description of Phuwiangvenator and Vayuraptor based on the data set used by Apesteguía and colleagues in their 2016 description of Gualicho. In their analysis, they added the two new taxa from their description as well as the contemporaneous theropod Siamotyrannus and removed the problematic Santanaraptor from their data set. They recovered Phuwiangvenator as a basal member of megaraptora with the following synapomorphies for the group: a ventral groove on the first manual phalanx, a transversely compressed first manual ungual, a prominence on the anterior surface of the distal end of the tibia, a lateral extension of the astragalus, and a flattened sacrum. Notably, they recovered Vayuraptor as a non-megaraptoran coelurosaur, which has not been recovered by subsequent analyses. The strict consensus tree from their analysis is shown below.
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