Phuwiangvenator

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Phuwiangvenator
Temporal range: Early Cretaceous[1]
~125 to 120 Ma - Late Barremian
↓
The finger bones of the holotype of Phuwiangvenator
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Clade: †Megaraptora
Genus: †Phuwiangvenator
Samathi et al., 2019
Type species
†Phuwiangvenator yaemnioymi
Samathi et al., 2019

Phuwiangvenator (

paleontologist from Thailand and the first person to discover fossils there.[2]

Discovery

A map of Thailand with the location of the Phu Wiang locality in the inset

The

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.[2]

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.[1] One of the metatarsals was later discovered to contain a fracture, which was studied and published on in 2023.[3]

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.[2]

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

theropod.[2]

Vertebrae

Phuwiangvenator is only known from four vertebrae, one from the

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.[2]

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.[2]

The preserved toe bones and claws of Phuwiangvenator
Legs

The leg bones share numerous marked similarities with other

megaraptorids.[1]

Classification

Phylogeny

Samathi and colleagues performed a

coelurosaur, which has not been recovered by subsequent analyses.[2][4] The strict consensus tree from their analysis is shown below.[2]

Coelurosauria

The most recent phylogenetic analysis to include Phuwiangvenator was the one which accompanied the description of Maip in 2022. The analysis of the authors, led by Alexis Aranciaga Rolando, included every taxon confidently assigned to megaraptora including an unnamed specimen from the Griman Creek Formation (called the "Lightning Claw" by some publications) and another unnamed specimen from the Bajo Barreal Formation. Their analysis of Megaraptora differs from the initial only in the exact classification of Vayuraptor and the inclusion of more taxa, which the authors state led to a more resolved tree consistent with previous analyses.[4]

Coelurosauria

Possible synonymity

The known material of Siamotyrannus, which coexisted with Phuwiangvenator

There are three mid-sized

centra of Siamotyrannus are much more convex than in Phuwiangvenator.[2]

The distinctions between Phuwiangvenator and Vayuraptor which they outline are as follows: the cranioproximate process of the astragalus is much more pronounced in Vayuraptor and they note that Vayuraptor had two grooves on the body of the astragalus whereas Phuwiangvenator only had one. The final distinction between the two are the lack of an upward curving process of the lateral condyle in Vayuraptor, which is one of the autapomorphies of Phuwiangvenator. This last trait was also observed in all ontogenetic stages of Allosaurus, which the authors state implies that the absence of this trait in Vayuraptor means that the distinction is probably not the result of ontogeny.[2]

Paleobiology

Arm musculature

In 2023, Alexis M. Aranciaga Rolando and colleagues published an analysis of the inferred forelimb musculature of

unguals of Phuwiangvenator and those of younger megaraptorans like Megaraptor, Maip, and Australovenator. These differences are concentrated in the first finger of the hand, which in derived megaraptorans hosts a single giant claw which is presumed to have served a purpose in hunting or feeding. The first claw of Phuwiangvenator lacks the well-developed furrows which are present on the proximal extension of the claw. In other species, these are thought to have been attachment sites for powerful muscles, enabling greater control and flexibility of the finger movements of these animals.[6]

Pathology

The metatarsals of the holotype, with the fracture visible (B5)

One of the

computer tomography led the authors to conclude that the animal was not yet fully grown when it died.[3]

Samathi and colleagues suggest several possible causes of the fracture. They first suggest a blow from the tail club of an

ankylosaur, but they discard this hypothesis because no ankylosaur remains are known from the Early Cretaceous of Thailand. Possible competition or combat with another large theropod is also suggested, because there are several large theropods known from nearby localities, but they state that there is no direct evidence for this and it is impossible to determine without additional evidence. They conclude that the most likely explanation is that the animal hit its foot into a hard object such as a rock or possibly fell over to cause the type of incomplete fracture which is observed.[3]

Evidence for severe pathologies being healed has been used by some authors to infer herding behavior in extinct animals. There are known associations of large theropods (i.e. Albertosaurus and Mapusaurus), so the authors state that it is possible that Phuwiangvenator exhibited similar behaviors. However, they also suggest that the animal may have simply survived for a short time after the injury and lived with a limp.[3]

Paleoecology

Diet

None of the skull of Phuwiangvenator has been preserved, but the animal is presumed to have been carnivorous. However, it does not have the same specialized arm musculature to aid in feeding as other megaraptorans.[6]

Paleoenvironment

A life reconstruction of some animals which coexisted with Phuwiangvenator

The

braided channels.[7][10]

Contemporary fauna

Of all the

ornithischians discovered from the formation.[8]

Freshwater life is abundant in the Sao Khua Formation. These include the

bivalves.[10] There is also an indeterminate pterosaur known from the formation.[14]

See also

References

  1. ^
    S2CID 244363244
    .
  2. ^
    doi:10.4202/app.00540.2018
    .
  3. ^
    S2CID 255902629
    .
  4. ^
    PMID 35474310
    .
  5. PMID 27410683
    .
  6. ^
    S2CID 255939861
    .
  7. ^
    S2CID 249702713
    .
  8. ^
    ISSN 0031-0182
    .
  9. ISBN 978-1862395633
    .
  10. ^ a b Eric, Buffetaut; Varavudh, Suteethorn (1998). Hall, Robert; Holloway, Jeremy D. (eds.). "The biogeographical significance of the Mesozoic vertebrates from Thailand". Biogeography and Geological Evolution of SE Asia. Leiden, The Netherlands: Backhuys Publishers: 83–90.
  11. ^
    S2CID 233884025
    .
  12. ^ Buffetaut, Eric; Suteethorn, Varavudh (January 2012). "A carcharodontosaurid theropod (Dinosauria, Saurischia) in the Sao Khua Formation (Early Cretaceous, Barremian) of Thailand". 2012 EAVP Abstracts: 27–30.
  13. ^ Buffetaut, Eric; Suteethorn, Varavudh; Le Loeuff, Jean; Khansubha, Sasa-On; Tong, Haiyan; Wongko, K. (January 2005). "The dinosaur fauna from the Khok Kruat Formation (Early Cretaceous) of Thailand". International Conference on Geology, Geotechnology and Mineral Resources of Indochina (GEOINDO 2005): 575–581.
  14. ^ Cuny, Gilles; Suteethorn, V. (2003-01-01). "A Pterodactyloid tooth from the Sao Khua Formation (Early Cretaceous) of Thailand". Mahasarakham University Journal. 22: 92–98.
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