Phuwiangvenator yaemniyomi and Vayuraptor nongbualamphuensis

Two new species of theropod dinosaur have been described from partial fossil remains excavated from strata associated with the Sao Khua Formation of north-eastern Thailand.  It is likely that both these meat-eating dinosaurs have affinities with the Megaraptora and their discovery lends weight to the idea that the Megaraptoridae and their near relatives probably originated in Asia.  The dinosaurs have been named Phuwiangvenator yaemniyomi and Vayuraptor nongbualamphuensis, Phuwiangvenator has been described as a megaraptoran whilst the exact taxonomic position of Vayuraptor remains uncertain, although the authors of the scientific paper suggest that it too was a member of the clade of dinosaurs with long-snouts, highly pneumatised skeletons and with large claws.

Bones in Approximate Life Position from the Right Foot of P. yaemniyomi

Bones and claws from the right foot of Phuwiangvenator yaemniyomi with an accompanying line drawing.

Picture Credit: Samathi et al

Lower Cretaceous Carnivorous Dinosaurs

The fossils were found nearly twenty-five miles apart, but the strata in which the fragmentary fossil material was found is contemporaneous and dated to the upper Barremian stage of the Lower
Cretaceous.  The first identified specimens of P. yaemniyomi were found by Preecha Sainongkham, a team member at the Phu Wiang Fossil Research Centre and Dinosaur Museum back in 1993.  The Phu Wiang Mountain region is highly fossiliferous and numerous vertebrate fossils representing the fauna of a low-lying, inland, lacustrine environment have been discovered over the years.  The first dinosaur bone known from Thailand was found in 1976, a scrappy bone fragment that was assigned to the Sauropoda.  This fossil was found by Sudham Yaemniyom, who was at the time a geologist with the country’s Department of Mineral Resources, Bangkok.  The species name of Phuwiangvenator yaemniyomi honours his contribution to the geology and palaeontology of Thailand.

Phuwiangvenator is the larger of the two Theropods, it is believed to have measured around 5.5 to 6 metres in length.  It is known from dorsal and sacral vertebrae plus elements of the hind limbs and feet.  All the fossil material was found within the same bedding plane and within an area of just 5 square metres.

Views of the Right Tibia (A1 – A6) and a Proximal View of the Left Tibia (P. yaemniyomi)

Right tibia (A) in various views with a proximal view (B) of the left tibia – Phuwiangvenator yaemniyomi.

Picture Credit: Samathi et al

Vayuraptor nongbualamphuensis – Raptor of the Wind God

The fossils associated with Vayuraptor were found in 1988.  It is known from a left tibia and ankle bones.  The genus name is from the Sanskrit for “Vayu”, a God of the Wind and the Latin term “raptor”, which means thief.  Analysis of the single lower leg bone indicates that like Phuwiangvenator, this dinosaur was a fast-running, cursorial predator.  The fossils of both dinosaurs are now part of the extensive dinosaur fossil collection at the Sirindhorn Museum in Kalasin Province.  This museum houses the largest collection of dinosaur fossil bones in north-eastern Thailand.

Analysis of the Tibia Suggests that Vayuraptor was a Fast Runner

Vayuraptor nongbualamphuensis views of the left tibia and ankle (A5 and A6).

Picture Credit: Samathi et al

Megaraptora Originated in Asia

The establishing of at least one of these dinosaurs as a member of the Megaraptora clade, possibly both, helps to support the hypothesis that in south-eastern Asia during the Early Cretaceous, it was the Megaraptora that were diverse and playing the role of apex predators.  This is in contrast to other ecosystems elsewhere in the world, that were dominated by different kinds of theropod dinosaur.  A basal member of the Megaraptora, Fukuiraptor kitadaniensis is known from the Lower Cretaceous (Barremian) of Japan, these two dinosaurs are also (most likely), from the Barremian.  Their identification supports the idea that these fast running, lightly built predators evolved in Asia.

A Model of the Basal Megaraptoran  Clade – Fukuiraptor

CollectA Fukuiraptor model.  It is likely that Phuwiangvenator yaemniyomi and Vayuraptor nongbualamphuensis were similar to Fukuiraptor kitadaniensis.

Picture Credit: Everything Dinosaur

An Early Cretaceous Heyday for the Megaraptorans

Fossils of this type of meat-eating dinosaur have been reported from the Barremian to the Aptian faunal stage of the Early Cretaceous.  The authors of the scientific paper, published in the scientific journal “Acta Palaeontologica Polonica”, note that several specimens of megaraptoran dinosaurs have been recorded from the Aptian of Australia and one reported from the later Albian faunal stage of South America.  Megaraptorans are known from the Late Cretaceous but seem to indicate that by around 90 million years ago, “megaraptors” had a more limited range and seem to have been confined mostly to South America.

A Typical Illustration of a Member of the Megaraptoridae Family of Theropod Dinosaurs

A leggy, Late Cretaceous carnivore (Murusraptor).  Roaming Patagonia around 80 million years ago.  By the Late Cretaceous the Megaraptoridae may have been less widespread and more provincial.

Picture Credit: Jan Sovak (University of Alberta)

A spokesperson from Everything Dinosaur commented:

“The identification of these theropod remains that had been known about for more than twenty-five years, has been partially resolved.  Hopefully, more fossil material associated with the Vayuraptor genus will be found in Thailand so that it too can be more definitively placed within the Megaraptora clade.  Given the extent of the fossil discoveries made from the Phu Wiang Mountain region thus far, it is highly likely that more new dinosaurs will be named and described from Thailand in the future.”

To read an article about a Late Cretaceous member of the Megaraptoridae family from South America that was reported upon in 2018: A New Member of the Megaraptoridae from the Late Cretaceous of South America (Tratayenia rosalesi)

The scientific paper: “Two new basal coelurosaurian theropod dinosaurs from the Lower Cretaceous Sao Khua Formation of Thailand” by A. Samathi, P. Chanthasit and P. Martin Sander published in  Acta Palaeontologica Polonica.

Mussaurus Switched from Four Legs to Two

A team of scientists, including researchers from the Royal Veterinary College based in London and Museo de La Plata and National Scientific and Technical Research Council (CONICET) located in Argentina, have collaborated to produce a report on how a Late Triassic sauropodomorph changed as it grew up.  The dinosaur in question Mussaurus patagonicus is an ideal candidate for dinosaur growth studies as it is known from numerous partial to nearly complete skeletons from hatchlings to fully grown adults.  Writing in the academic journal the researchers conclude that Mussaurus could only move on four limbs once born but switched to two legs as it grew up, just as our species switches from all fours to bipedal walking as we grow.

Scientists Looked at How the Centre of Mass Changed in the Body of Mussaurus to Work Out How it Walked

Mussaurus specimens. (a, b) hatchling, (c) yearling and (bottom) adult.  Scale bars represent 5 cm (a), (b) 15 cm (c) and 100 cm in the adult animal representation.

Picture Credit: Scientific Reports

An Argentinian Sauropodomorph

Fossils of Mussaurus come from southern Argentina, at birth this dinosaur was only a few centimetres in length, but it reached its adult size in around eight years.  Essentially, this dinosaur went from weighing about 60 grams to weighing an estimated 1,300 kilograms with a body length of approximately 8 metres.  The research team conclude that it might have barely been able to walk or run on two legs at the age of one, but would have only committed to being bipedal once it reached adulthood.  This study has implications for the largest terrestrial vertebrates that ever lived as Mussaurus is regarded as an ancestral form of the later sauropods, giants like Apatosaurus, Mamenchisaurus and Giraffatitan, that were to evolve in the Jurassic.

The team scanned key fossils of Mussaurus into three-dimensional models, connected the bones into digital skeletons, and added soft tissue to estimate the shape of the body and its major segments such as head, neck, torso, tail and limbs.  These computer models were then used to estimate the location of the animal’s centre of mass, the point at which all weight can be assumed to act through.  This estimate enabled the scientists to then test whether different models representing different growth stages of Mussaurus patagonicus could have stood on two legs or not, because the centre of mass must be placed under the feet in such poses.

Identifying the Centre of Mass as Mussaurus Grew Up

Plotting the ontogeny of Mussaurus (a) hatchling, (b) yearling and (c) adult animal and the subsequent effect on centre of mass and locomotion.

Picture Credit: Scientific Reports

From Four Legs to Two

One of the authors of the scientific paper, Dr Alejandro Otero (CONICET) stated:

“Mussaurus switched from four legs as a baby to two legs by adulthood, much as humans do.  It is important to notice that such locomotor switching is rare in nature and the fact that we were able to recognise it in extinct forms like dinosaurs highlights the importance of our exciting findings.”

Professor John Hutchinson of the Royal Veterinary College, an expert in animal locomotion and co-author of the paper commented:

“We created the first 3-D representation of the major changes of body form and function across the growth of a dinosaur.  And we were surprised to learn that enlargement of the tail and reduction of the neck had more of an effect on how Mussaurus stood than how long its forelimbs were, which is what people used to think.”

Implications for Giant Dinosaurs

At around eight metres in length, Mussaurus was one of the largest dinosaurs in southern South America during the Late Triassic (estimated to be Norian faunal stage), however, during the Jurassic and Cretaceous much larger lizard-hipped dinosaurs would evolve from this lineage.  By improving our understanding about how some of the sauropodomorphs moved this type of research can provide insights into how much bigger plant-eating, long-necked giants walked.  When adult, dinosaurs such as Diplodocus and Brachiosaurus were very much quadrupedal, although it has been suggested that when very young some of these dinosaurs might have been able to rear up onto their hind legs to escape danger.*

Mussaurus Scale Comparison

Mussaurus scale drawing compared to an adult human and the skeleton of a typical Late Jurassic sauropod.

Picture Credit: Scientific Reports with additional annotation and information from Everything Dinosaur

* To read an article from 2011 that looked at the research into trace fossils from the western United States that hinted that some very young sauropods may have been able to run on just their hind legs: Facultative Bipedalism in Sauropods

The research team hope to build on this work as they plan to use computer models to replicate in greater detail how Mussaurus may have actually moved, such as how fast it could walk or run.

Everything Dinosaur acknowledges the assistance of a press release from the Royal Veterinary College (London) in the compilation of this article.

The scientific paper: “Ontogenetic changes in the body plan of the sauropodomorph dinosaur Mussaurus patagonicus reveal shifts of locomotor stance during growth” by Alejandro Otero, Andrew R. Cuff, Vivian Allen, Lauren Sumner-Rooney, Diego Pol and John R. Hutchinson published in Scientific Reports.