A team of international researchers has named a remarkable new species of long-necked dinosaur from Thailand. Uragasaurus kalasinensis is the first formally described member of the Mamenchisauridae from Thailand. Although the fossil evidence consists of a single vertebra, the bone preserves a unique combination of anatomical features that enabled scientists to identify an entirely new dinosaur.  It is the fifteenth dinosaur to be named from fossils discovered in Thailand.

The research, published as an open-access paper in the journal “Scientific Reports”, highlights the growing importance of Thailand in helping palaeontologists understand the evolution and distribution of giant sauropod dinosaurs during the Late Jurassic.

Uragasaurus kalasinensis and the Mamenchisauridae

The newly described dinosaur lived approximately 145–150 million years ago during the Late Jurassic. Its fossil was recovered from the Phu Noi locality in Kalasin Province, north-eastern Thailand, within the Phu Kradung Formation.

Mamenchisaurids are famous for their extraordinarily long necks. Most known mamenchisaurids have been discovered in China, so the identification of Uragasaurus kalasinensis (pronounced You-rah-ga-sore-us cal-ah-sin-en-sis), considerably extends the confirmed geographical distribution of this distinctive group.

Scientists estimate that Uragasaurus measured around twenty metres in length and was a huge plant-eater that browsed vegetation growing high above the ground. Its neck has been described as being as long as a cricket pitch.

A herd of Uragasaurus kalasinensis feeding in a Late Jurassic forest in Thailand. A metriacanthosaurid theropod can be seen in the background along with a pair of rhamphorhynchoid pterosaurs. Picture credit: Pakorn Chotchaiyaporn.

Picture credit: Pakorn Chotchaiyaporn. Licensed under a Creative Commons Attribution 4.0 International License.

A Single Vertebra Tells an Extraordinary Story

The fossil consists of an anterior dorsal vertebra. At first glance, naming a dinosaur from just one bone might seem surprising. However, vertebrae contain numerous anatomical characteristics that are extremely useful for identifying different dinosaur groups. Individual sauropod vertebrae often preserve unique anatomical characteristics that enable researchers to recognise and describe new species.

The researchers carefully compared the fossil with vertebrae belonging to many other Asian sauropods. They found a unique arrangement of bony ridges, cavities and supporting structures, known as laminae, which had not previously been documented in any recognised species. This distinctive combination of features justified the establishment of the new genus Uragasaurus.

The holotype anterior dorsal vertebra of Uragasaurus kalasinensis (PRC 460) in anterior (a) and posterior (b) views. Digital rendering of the specimen in anterior (c), posterior (d), right lateral (e), left lateral (f), dorsal (g), and ventral (h) views. Asterisk refers to an autapomorphic character. The blue highlight indicates the pneumatic fossa and pleurocoel. Picture credit: Nilpanapan et al.

Picture credit: Nilpanapan et al. Licensed under a Creative Commons Attribution 4.0 International License.

A Growing Picture of Thailand’s Dinosaur Fauna

Thailand has become increasingly important for dinosaur research over the last three decades. Numerous excavations have revealed an impressive diversity of prehistoric animals, including theropods, ornithopods and several species of sauropod.

To read an article from 2019 highlighting the discovery of two new theropod species from north-eastern Thailand: Two New Theropod Dinosaurs from Thailand.

The discovery of Uragasaurus kalasinensis demonstrates that north-eastern Thailand preserves fossils of dinosaur groups previously thought to be largely restricted to China. It also suggests that mamenchisaurids dispersed more widely across eastern Asia than palaeontologists had previously appreciated. The researchers propose that continued exploration of the Phu Kradung Formation is likely to reveal additional fossils that will help clarify the evolutionary history of these spectacular long-necked dinosaurs.

The giant Nagatitan chaiyaphumensis, the fourteenth dinosaur to be described from Thailand: The Last Titan from Thailand.

A Single Vertebra Can Rewrite Dinosaur History

While complete dinosaur skeletons understandably capture the public imagination, they are extremely rare. Discoveries such as Uragasaurus kalasinensis remind us that experienced palaeontologists can extract an enormous amount of scientific information from isolated bones. Careful anatomical comparisons often reveal evolutionary relationships that would otherwise remain hidden.

A comparison of the anterior dorsal vertebrae of Uragasaurus kalasinensis with other Late Jurassic mamenchisaurids. Mamenchisaurus youngi (Upper Shaximiao Formation of Sichuan, China) and Mamenchisaurus hochuanensis (Upper Shaximiao Formation of the Chongqing municipality, China). Abbreviations lprdl, lower prezygodiapophyseal lamina; uprdl, upper prezygodiapophyseal lamina. Other abbreviations can be found in the second image in this article.  Asterisk refers to an autapomorphic character. The blue highlight indicates the pneumatic fossa and pleurocoel. Note images are not to scale. Picture credit: Nilpanapan et al.

Picture credit: Nilpanapan et al. Licensed under a Creative Commons Attribution 4.0 International License.

A Significant Discovery

The description of Uragasaurus kalasinensis represents another important milestone for Southeast Asian palaeontology. The discovery strengthens evidence that Thailand preserves an exceptionally important record of Jurassic dinosaurs and demonstrates that many new species remain to be discovered.

As fieldwork continues across the region, further fossil discoveries are likely to improve our understanding of how giant sauropods evolved and dispersed across Asia during the Jurassic.

Commenting on the research, Mike from Everything Dinosaur said:

“This fascinating study demonstrates how even a single fossil bone can significantly improve our understanding of dinosaur evolution. Thailand continues to produce scientifically important discoveries, and Uragasaurus kalasinensis adds another impressive dinosaur to the country’s growing fossil record.”

The scientific paper: “A new mamenchisaurid sauropod from the Lower Phu Kradung Formation, Upper Jurassic of northeastern Thailand” by Apirut Nilpanapan, Sita Manitkoon, Varavudh Suteethorn and Komsorn Lauprasert an open-access paper published in Scientific Reports.

A new study examining Tyrannosaurus rex hatchlings has provided fresh insight into the early lives of these famous theropod dinosaurs. Researchers writing in the journal “Biology” investigated evidence linked to the development and reproductive strategies of large meat-eating dinosaurs.  The researchers concluded that tyrannosaurs produced relatively small hatchlings compared to modern birds. This suggests that they laid large numbers of eggs and invested less energy in caring for their young.

Although adult Tyrannosaurus rex specimens are amongst the most famous fossils ever found, the earliest growth stages remain poorly understood. Fossils of very young tyrannosaurs are exceptionally rare. Therefore, palaeontologists continue to search for clues about how these remarkable animals developed.

The beautiful Tristan the Tyrannosaurus rex skull shown in lateral view. A new study suggests different niches in the ecosystem for juvenile tyrannosaurs compared to the adult animals. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

Studying Tyrannosaurus rex Hatchlings

The enormous size of adult T. rex raises fascinating questions about reproduction. Every giant dinosaur began life as a small hatchling.  All dinosaurs emerged from eggs. Consequently, scientists want to understand how these animals grew from vulnerable juveniles into apex predators.

The scientists, which included researchers from the University of Bath, examined fossil evidence and compared growth patterns seen in related dinosaurs. This work helps palaeontologists build a more complete picture of tyrannosaur biology. Dinosaurs occupied an evolutionary position between more primitive reptiles and modern birds, both in their anatomy and in some aspects of their biology such as reproduction strategies.

Young tyrannosaurs would have looked very different from adults. They were probably lightly built, long-legged animals adapted for speed. In contrast, mature T. rex individuals developed huge skulls, powerful jaws and immense bite forces.

This dramatic transformation demonstrates how dinosaurs could occupy different ecological roles during their lives.

Tyrannosaur hatchlings had very different body proportions compared to adults. A new study provides fresh insights into tyrannosaur reproduction strategies. Picture credit: Everything Dinosaur (AI Assisted).

Picture credit: Everything Dinosaur (AI Assisted)

Understanding Dinosaur Growth and Reproduction

The study also highlights the challenges associated with investigating dinosaur reproduction. Unlike modern birds and reptiles, palaeontologists cannot directly observe extinct dinosaurs nesting or raising their young.

Instead, scientists rely on fossils, bone histology, eggs, embryos and comparisons with related, extant animals. Dinosaur reproductive strategies probably represented an intermediate stage between more primitive reptiles, such as crocodilians which typically provide limited parental care, and modern birds. Birds often demonstrate advanced parental behaviours and significant investment in their offspring.

Evidence from other theropod dinosaurs shows that many species grew rapidly. This fast growth helped them reach larger sizes more quickly and may have reduced the risks faced by young animals.

From Tiny Hatchling to Apex Predator

An adult Tyrannosaurus rex could reach more than twelve metres in length. However, newly hatched individuals would have been tiny compared to their parents. The research team studied bones and teeth of hatchlings from the Frenchman Formation of Saskatchewan (Canada). These fossils reputedly represent T. rex. In addition, juvenile tyrannosaur fossils from the geologically older Dinosaur Provincial Park formation were studied. These fossils have been assigned to Gorgosaurus.

The difference between hatchlings and adults suggests that young tyrannosaurs may have hunted different prey. This reduced competition between generations and allowed animals of different ages to exploit separate ecological niches. Indeed, the contrasting body shapes between juvenile and mature tyrannosaurs fuelled the Nanotyrannus debate.  However, recent studies have concluded that lightly built, long-legged tyrannosaurs thought to represent T. rex juveniles are most likely a different tyrannosaur taxon.

To read more about the recent Nanotyrannus research: New Paper Reinforces Nanotyrannus Unique Taxon Theory.

This idea, animals of the same species filling different niches depending on their age is known as ontogenetic niche partitioning, has been proposed for several dinosaur groups.

Revealing the Early Lives of Famous Dinosaurs

The study of Tyrannosaurus rex hatchlings remains an exciting area of palaeontology. For example, in this paper, the researchers stated that synchrotron scans revealed Haversian bone re-modelling, suggesting that tyrannosaurs moved soon after hatching.  It is speculated that tyrannosaurs may have been precocial.  Precocial young are relatively mobile and independent soon after hatching.

A 2021 article that highlights a study suggesting that baby tyrannosaurs were precocial: Tyrannosaurs – Born Ready to Hunt!

Future fossil discoveries may reveal more information about nesting behaviour, growth rates and juvenile anatomy.

Everything Dinosaur team members regularly highlight that even the most famous dinosaurs continue to surprise scientists. New research techniques and fossil discoveries are helping experts build a clearer picture of how these extraordinary animals lived. Understanding the youngest members of this species provides valuable information about one of the most remarkable predators in Earth’s history.

A dinosaur egg (believed to be from a theropod dinosaur). Theropod dinosaur eggs tend to be elongated and less round compared to the eggs of other dinosaurs such as sauropods. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

Estimating Nest Sizes

Clutch sizes were likely large. The team conservatively estimated that a small, female adult T. rex would lay around twenty eggs. The largest T. rex females could perhaps lay thirty eggs. In comparison, Gorgosaurus (G. libratus), may have laid more eggs per clutch. For example, the researchers propose clutch sizes of up to a hundred eggs for Gorgosaurus.

Scientists can only speculate about the mortality rate of hatchling tyrannosaurs. However, animals that produce large numbers of offspring typically experience high juvenile mortality rates. Many predators could have killed a baby T. rex. For example, hatchlings had to avoid dromaeosaurs, crocodilians and the powerful beaks of azhdarchid pterosaurs.

The scientific paper “Hatchlings of Tyrannosaurus rex and the Evolution of Dinosaur Reproductive Strategies” by Nicholas R. Longrich, Peter J. Makovicky, Tim Tokaryk, David M. L. Cooper, Evan T. Saitta, Gregory M. Erickson, Tamas Szekely and Eric Snively published in Biology.

The Everything Dinosaur website: Models of Theropods and Other Dinosaurs.

The study of Thylacoleo carnifex anatomy has revealed one of the most unusual mammalian predators known to science. Often called the “marsupial lion”, this apex predator was not a member of the cat family.  Indeed, its closest living relatives are wombats and koalas. Despite evolving from primarily plant-eating ancestors, Thylacoleo carnifex became a highly specialised carnivore. Its powerful jaws, extraordinary teeth and muscular body made it a significant predator of the Pleistocene Epoch.  Early studies suggested that it may have been frugivore (fruit eater), or that it was a scavenger.  However, more modern interpretations depict Thylacoleo carnifex as a hypercarnivore.

Understanding Thylacoleo carnifex Anatomy

The first fossils of Thylacoleo carnifex were scientifically described in the 19th century. Since then, more complete fossil discoveries have transformed our understanding of this animal. Older reconstructions often depicted Thylacoleo as cat-like. However, detailed studies show that this marsupial had a very different body plan. It combined tremendous strength with adaptations for climbing, gripping and ambushing prey.

A large individual may have measured around 1.5 metres long. Many adults probably weighed between 100 and 130 kilograms, although exceptionally large specimens may have approached 160 kilograms. Larger individuals may represent males, suggesting possible sexual dimorphism. After all, sexual dimorphism is seen in extant relatives of this species.

This extinct marsupial continues to inspire scientists and palaeoartists.  For instance, it has featured on the front cover of the prestigious “Prehistoric Times” magazine.

The front cover features a Marsupial lion. Thylacoleo carnifex features on the front cover art of “Prehistoric Times” magazine issue 85. Picture credit: Mike Fredericks.

Picture credit: Mike Fredericks

A Powerful Skull and an Incredible Bite

The skull of Thylacoleo carnifex was short, broad and extremely robust. Huge jaw muscles helped generate a tremendous bite force. Indeed, studies suggest that relative to body size, Thylacoleo possessed one of the most powerful bites of any known mammalian predator. The eyes faced forwards, providing binocular vision. This adaptation would have helped with judging distance when attacking prey. Consequently, palaeontologists often interpret Thylacoleo as an ambush hunter rather than a pursuit predator.

The Remarkable Teeth of Thylacoleo carnifex

One of the most fascinating aspects of Thylacoleo carnifex anatomy is the dentition. Unlike felids, Thylacoleo did not rely on large canine teeth to despatch prey. Its upper canines were small and rounded, whilst the lower jaw lacked canine teeth entirely.

The dental formula of T. carnifex:

• Upper jaw (each side): 3 incisors, 1 canine, 3 premolars and 1 molar
• Lower jaw (each side): 1 incisor, no canines, 3 premolars and 2 molars.

The lower incisors were enlarged, chisel-shaped and projected forwards.  In addition, fossils show extensive wear. The enormous third premolars were highly specialised. They acted like shears and were functionally similar to the carnassial teeth found in modern carnivorous mammals.

No living predator has a set of teeth quite like Thylacoleo carnifex.

To read an article about the discovery of an ancestor of the “marsupial lion”: Attenborough’s New Kitty.

Strong Forelimbs and a Deadly Thumb Claw

The forelimbs of Thylacoleo were exceptionally powerful. The shoulders and front legs were heavily muscled, suggesting an animal that relied on strength to subdue prey. Furthermore, the manus (hand) had five digits, each equipped with a claw. The first digit, equivalent to a thumb, was particularly remarkable. It was semi-opposable and carried a large, strongly curved claw.

This enlarged claw was probably used to grip prey and assist with climbing. It may have been protected when not in use, although it worked differently from the retractable claws of modern cats.

A Marsupial Built for Power Not for Speed

The body of Thylacoleo carnifex was compact and muscular. It had a deep chest, broad shoulders and a relatively short back. Its body proportions suggest that this predator was not built for chasing prey over long distances. Instead, it was adapted for explosive power, climbing ability and controlling struggling animals. The hind feet provide further evidence that Thylacoleo was no cat-like predator. It walked with the sole of the foot contacting the ground, a posture known as plantigrade locomotion. Bears and humans also use this type of stance.

The potential maximum velocity of Thylacoleo remains unknown.  The combat bodies of extant wombats (see image below) share many characteristics with their close relatives (Thylacoleonidae).  At first sight, these animals might look like they are incapable of running at speed.  However, appearances can be deceptive.  Wombats have been recorded running at twenty-five miles per hour (forty kilometres per hour) over short distances.

Like other diprotodontian marsupials, the second and third toes were probably fused together.

Thylacoleo is classified as a member of the Diprotodontia suborder the Vombatiformes. Extant wombats such as this forest wombat (Vombatidae family) are closely related to marsupial lions (Thylacoleonidae).

Picture credit: Everything Dinosaur

The Tail of Thylacoleo carnifex

For many years, the tail of Thylacoleo was poorly understood. However, more complete fossil discoveries have revealed that this predator had a long and muscular tail.

The tail may have provided extra support when the animal reared upwards. This “tripod” posture is seen in some living marsupials.

Some Australian rock art has been suggested to represent Thylacoleo. These interpretations remain debated, but they raise interesting questions about the external appearance of this extinct animal. For example, there could have been a tuft on the end of the tail.

Did Thylacoleo carnifex Hunt Diprotodon?

Thylacoleo carnifex shared its environment with many famous Australian megafauna species, including the giant marsupial Diprotodon optatum. Diprotodon was the largest marsupial known to science. A fully-grown male Diprotodon had a shoulder height of approximately 1.8 metres.  It weighed around three tonnes, around twenty-five times heavier than Thylacoleo.

However, Thylacoleo may have targeted young, injured or vulnerable individuals. Its powerful forelimbs, gripping claws and devastating bite would have made it a dangerous predator.  The CollectA Deluxe Diprotodon, introduced in 2024 shows some remarkable detail.  For example, the top of the left hind limb reveals an old scar from an attack from a Thylacoleo. The scars are old suggesting an attack when this Diprotodon was much younger.

Whilst speculative, it is interesting to note that CollectA added this detail, a speculation on a predator/prey relationship.

The CollectA Diprotodon model has an old scar from a marsupial lion on its rump.

The relationship between these two iconic marsupials highlights the complexity of prehistoric Australian ecosystems.

To view the CollectA Deluxe model range: CollectA Deluxe Age of Dinosaurs.

Thylacoleo carnifex Anatomy Reveals A Unique Australian Predator

Research into Thylacoleo carnifex anatomy continues to demonstrate how unusual this animal was. It was not simply Australia’s version of a big cat. Instead, evolution produced a completely different type of predator. Indeed, several species have been classified, tracing the origins of these bizarre carnivores back into the Oligocene Epoch.

To read a blog post outlining ideas into Thylacoleo hunting strategy: How the Marsupial Lion Got to Grips with its Prey.

Mike from Everything Dinosaur commented:

“With its powerful front limbs, extraordinary teeth and specialised hunting adaptations, Thylacoleo remains one of the most fascinating mammals to have ever lived.  Thylacoleo carnifex died out around 40,000 years ago.  Modern humans would have encountered it.  Imagine viewing a living Thylacoleo!  I am sure this creature would have had a special status amongst those hunter gatherers that shared its environment.”

The award-winning Everything Dinosaur website: Dinosaur Toys and Prehistoric Animal Models.