A newly named giant Tylosaurus species has been named by researchers.  The new species of Tylosaurus has been erected based on fossils found in northern Texas. This enormous predator ruled the ancient seas around 80 million years ago (Campanian faunal stage of the Late Cretaceous).  The scientific paper was published in the Bulletin of the American Museum of Natural History. The new species has been named Tylosaurus rex.  Its name translates as “King of the Protuberance Lizards.”

The name also honours the work of Texas palaeontologist John Thurmond. Decades ago, he suspected these fossils represented a different species of Tylosaurus. Fossil material had previously been assigned to T. proriger.

The T. proriger fossil material mainly comes from Kansas. These fossils are estimated to be about 84 million years old. The Texas fossil material is around 4 million years younger. Geological age of the fossils strongly suggests that the Texas fossils do indeed represent a distinct species.

The new for 2026 CollectA Tylosaurus marine reptile model.  This new figure is based on Tylosaurus proriger.

The picture (above) shows the recently introduced CollectA Age of Dinosaurs Tylosaurus figure. We think that this model is based on T. proriger.

To view the CollectA Age of Dinosaurs models in stock: CollectA Prehistoric Life Models.

The research was led by scientists from the American Museum of Natural History (New York City), the Perot Museum of Nature and Science (Dallas, Texas), and Southern Methodist University (Texas).

A New Species – Tylosaurus rex

Tylosaurus rex was not a dinosaur. Media releases might have linked this mosasaur with Tyrannosaurus rex. However, the Tylosaurus genus is more closely related to modern snakes and lizards than it is to archosaurs like T. rex. Nevertheless, like Tyrannosaurus rex, Tylosaurus rex was probably an apex predator within its ecosystem. Mosasaurs were powerful ocean hunters. They evolved from land-dwelling lizards. Over time, they adapted fully to life in the sea.

The researchers estimate that Tylosaurus rex reached lengths of around 13 metres. Its huge skull contained strong jaws and serrated teeth. These adaptations helped it tackle large prey.

Lead author of the study Amelia Zietlow (American Museum of Natural History) commented that everything tends to be bigger in Texas, including mosasaurs.  Several autapomorphies were identified the allowed the research team to confidently reassign T. proriger material this new species.

A Violent Ancient Predator

One remarkable fossil specimen shows evidence of serious injuries. The animal had damage to its snout and jaw. Researchers think another giant Tylosaurus caused these wounds. In other words, these marine reptiles may have fought each other violently. Interestingly, this behaviour mirrors injuries found in Tyrannosaurus rex fossils. That similarity partly inspired the dramatic species name.

The Western Interior Seaway

During the Late Cretaceous, much of Texas lay beneath a shallow sea. This ancient waterway formed part of the famous Western Interior Seaway. The seas teemed with life. Giant sharks, fish, turtles and marine reptiles shared these waters.

Tylosaurus rex probably hunted almost anything it could overpower. Scientists think it likely preyed upon fish, turtles, and other marine reptiles.

Dramatic scene from the Western Interior Seaway painted by Burian. Picture credit: Zdeněk Burian.

Picture credit: Zdeněk Burian

Revisiting Old Fossils

This discovery highlights an important point in palaeontology. Museum collections can still contain unknown species. Some Tylosaurus rex fossils had sat in museum collections for decades. Researchers only recognised their true identity after careful re-examination. The study also updated mosasaur evolutionary data. According to the research team, scientists have relied on outdated datasets for many years.

As a result, this new study could reshape how researchers understand mosasaur evolution.

Mike from Everything Dinosaur commented”

“The discovery of Tylosaurus rex demonstrates how much there is still to learn about Russellosaurina clade of mosasaurs. Many spectacular fossils remain hidden in museum collections. Furthermore, new technology and fresh analysis continue to reveal ancient secrets. This newly described giant mosasaur was one of the largest marine predators of its time. Without doubt, it would have been an intimidating sight in the ancient seas of Texas.”

The scientific paper: “A gigantic new species of Tylosaurus (Squamata, Mosasauridae) from Texas: and a revised character list for phylogenetic analyses of Mosasauridae” by Amelia R. Zietlow, Michael J. Polcyn and Ronald S. Tykoski published in the Bulletin of the American Museum of Natural History.

The award-winning Everything Dinosaur website: Marine Reptile and Other Prehistoric Animal Models.

Although T. rex forelimbs look tiny compared to its huge body and head, the arms of T. rex were still powerful and although they may not have played a role in prey capture and submission, they still had their uses. At Everything Dinosaur, we receive lots of questions about dinosaurs.  Frequently, the questions focus on theropod dinosaurs.  Moreover, we tend to get quizzed on the “King of the Tyrant Lizards” – Tyrannosaurus rex.  For example, we often get asked why did T. rex have small arms?

Estimates of up to 9 tons in weight. A huge Tyrannosaurus rex skeleton cast on display.  Note the tiny arms which are disproportionately small. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

Why Did T. rex Have Small Arms?

This question has puzzled palaeontologists for many years. Indeed, when Barnum Brown first uncovered substantial fossil remains that were to lead to the erection of this genus, he thought the arm material found in association with the other theropod remains belonged to a different dinosaur. However, scientists now know that tyrannosaurs and other meat-eating dinosaur lineages that evolved a large body size, also evolved reduced forelimbs.

Tyrannosaurs, abelisaurs, carcharodontosaurids, megalosaurs and ceratosaurs are all theropod lineages that evolved reduced/vestigial forelimbs.  This is described as convergent evolution.  Numerous theories have been put forward. Recently, we wrote a blog post highlighting research that examined the relationship between theropod skull robustness and forelimb size. The study concluded that the tiny arms of some theropod dinosaurs evolved because their heads became the main weapons for subduing prey.

To read our blog post about a recently published academic paper that reviewed arm size and skull robusticity in theropod dinosaurs: New Study Solves Mystery of Tiny Theropod Arms.

The new for 2024 PNSO Tyrannotitan chubutensis dinosaur model. In the study into the relationship between skull robusticity and forelimb reduction, the second ranked theropod (behind T. rex) was Tyrannotitan chubutensis. This carcharodontosaurid was found to have an extremely robust and powerful skull, yet its forelimbs were extremely small.

Tyrannotitan chubutensis

In the research published in the “Royal Society Proceedings B”, the carcharodontosaurid Tyrannotitan chubutensis was found to rank second on the cranial robusticity scale developed by the scientists. Tyrannotitan lived millions of years before super-sized tyrannosaurs evolved.  This suggests that reduced forelimb adaptations evolved several times in the Theropoda.

Why did T. rex have small arms? One possible answer therefore is that jaws rather than claws become the most effective method of securing a meal.

Intriguingly, other theories have been put forward.  For instance, it has been suggested that reduced forelimbs evolved in theropods to help keep them out of the way when attacking another animal.  A Triceratops or Edmontosaurus for that matter would have been capable of inflicting severe damage to the arm of a tyrannosaur if it could bite it.  Perhaps, reduced forelimbs evolved to permit carnivorous dinosaurs to lunge headfirst at prey, without risking losing a limb.

Furthermore, if some theropods were pack hunters small limbs may have been an advantage when social feeding took place. Short arms helped reduce the risk of injury. Adult tyrannosaurs probably fed together at carcasses. Large, powerful predators snapping at each other could accidentally damage long forelimbs. Reduced forelimbs may have been safer in crowded feeding situations.

T. rex Arms Were Small but Strong

The arms of Tyrannosaurus rex were only about one metre long. However, palaeontologists think these limbs were heavily muscled. Each arm ended in two large claws. Studies suggest the forelimbs were strong.  They could have helped the animal to get up from a resting position, or perhaps they played a role in mating behaviour/courtship display. Some scientists think the arms helped hold struggling prey close to the body.

The PNSO 1:35 scale T. rex dinosaur model in a resting pose.  Getting up from a resting position might help answer the question why did T. rex have small arms?

Even though the arms seem small, they were not weak or useless.  They were probably held close to the body as shown in the picture (above) of the PNSO resting Tyrannosaurus rex figure. Indeed, the strong forelimbs and those tiny but robust two digits on each hand could have helped this dinosaur to stand upright after resting.

To view the range of PNSO models in stock: PNSO Scientific Art Figures.

Why Were the Arms So Short?

Scientists are still debating exactly why T. rex evolved such short forelimbs. The enormous skull and powerful jaws of T. rex may explain the reduced arm size. Its bite force was among the strongest of any land animal. As the head became larger and more specialised for hunting, the forelimbs may have become less important.

In simple terms, T. rex, like many other theropods probably relied on its jaws rather than its claws to capture prey.

Although small, the forelimbs probably still had a purpose. However, there is currently no single explanation accepted by all palaeontologists. Perhaps, the recently published paper evaluating theropod skull robusticity and forelimb reduction provides a plausible answer.

A Famous Dinosaur Mystery

Why did T. rex have small arms? It is a famous dinosaur mystery and a popular question.  Palaeontologists know that many different types of theropod dinosaur had reduced arms.  This is an example of convergent evolution.  The reduced forelimbs of theropod dinosaurs are one of their most fascinating features.

Mike from Everything Dinosaur commented:

“While scientists continue to study tyrannosaurs and other theropods it is clear that small forelimbs evolved independently in many theropod lineages.  Small arms must have had some form of evolutionary advantage as many theropods with reduced forelimbs were the apex predators in their ecosystems.”

The multi-award-winning Everything Dinosaur website: Scientifically Accurate Dinosaur Toys.

Why did T. rex have tiny arms?  This is a question we get asked a lot at Everything Dinosaur.  Ironically, several, not closely related theropod lineages show forelimb reduction. Tyrannosaurus rex had famously small arms, but so did lots of other large meat-eating dinosaurs. A new study suggests that the tiny arms of some theropod dinosaurs evolved because their heads became the main weapons for securing a meal.

The “Tristan” Tyrannosaurus rex specimen on display at the Museum für Naturkunde Berlin. This theropod has a huge skull and famously small arms. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

Why Did T. rex Have Tiny Arms?

This might be a popular question from model collectors. However, scientists tend to take a broader view. For example, if forelimb reduction is observed in the fossil remains of numerous theropods, then it could be concluded that reduced forelimbs evolved convergently. The new study published in the “Proceedings of the Royal Society B” examined eighty-two species of theropod dinosaur. Researchers found a strong link between powerful skulls and reduced forelimbs. In simple terms, as some meat-eating dinosaurs evolved stronger bites and more robust heads, their arms became less important.

The Everything Dinosaur Evolution Tyrannosaurus rex model (EDE001) shown in anterior view. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

The picture (above) shows the recently introduced Everything Dinosaur Evolution 1:33 scale Tyrannosaurus rex model shown in anterior view.  The forelimbs are in proportion, and they are barely noticeable compared to the deep, broad body and the huge head.

To view the range of Everything Dinosaur Evolution models: Everything Dinosaur Evolution Tyrannosaur Models.

The team developed a theropod cranial robusticity scoring system. Reduced or vestigial forelimbs evolved in at least five theropod lineages in concert with increased cranial robusticity and gigantism. Therefore, tiny arms evolved several times within the Theropoda.

Reduced/Vestigial Forelimbs Evolved Several Times

It is natural for most people to associate tiny arms with Tyrannosaurus rex. However, the scientists identified five different theropod lineages with reduced/vestigial forelimbs in animals with a large body mass.

• Tyrannosaurids
• Carcharodontosaurids
• Abelisaurids
• Megalosaurids
• Ceratosaurids

Importantly, these groups were not all closely related. Furthermore, it can be concluded that the same body plan evolved independently several times. This is known as convergent evolution.

The new for 2026 CollectA Deluxe Meraxes gigas figure. This replica of a super-sized carcharodontosaurid theropod had reduced forelimbs. This is an example of convergent evolution.

The giant carcharodontosaurid Meraxes gigas, fossils of which come from Upper Cretaceous deposits in Patagonia is another example of a large theropod with greatly reduced forelimbs. The picture (above) shows the new for 2026 CollectA Deluxe Meraxes model.  The tiny arms and small hands with three digits have been beautifully sculpted.

To view the CollectA Deluxe model range: CollectA Deluxe Prehistoric Animal Models.

Robust and Powerful Skull Replaced Strong Arms

The research team concluded that theropod skulls became increasingly important for attacking prey. As a result, the arms gradually reduced in size. Lead author Charlie Roger Scherer (University College London) explained that the head effectively “took over” from the forelimbs during hunting.

He stated:

“Everyone knows the T. rex had tiny arms but other giant theropod dinosaurs also evolved relatively small forelimbs. The Carnotaurus had ridiculously tiny arms, smaller than the T. rex. We sought to understand what was driving this change and found a strong relationship between short arms and large, powerfully built heads. The head took over from the arms as the method of attack. It’s a case of ‘use it or lose it’ – the arms are no longer useful and reduce in size over time.”

The scientists found that reduced forelimbs were more strongly linked to skull robustness than overall body size. This was a key discovery. Previously, some researchers suggested that small arms were simply a side effect of giant body size. However, the new study challenges that idea.

Some theropods with tiny arms were not especially huge. For example, Majungasaurus from the Late Cretaceous of Madagascar weighed around 1.6 tonnes. Although large, it had a body weight four times lighter than Tyrannosaurus rex. Despite this, it still had very reduced forelimbs and a heavily built skull.

Majungasaurus models from Haolonggood. The Deng Fei Majungasaurus figure is shown in lateral view with the blue-tailed Ou Peng shown on the right.  These abelisaurid theropods had a robust skull and tiny arms.

To view the Haolonggood range of prehistoric animals: Haolonggood Prehistoric Animal Figures.

An Evolutionary Arms Race

The researchers think gigantic prey animals may have driven this evolutionary trend. During the Jurassic and Cretaceous, enormous plant-eating dinosaurs (sauropods) dominated many ecosystems. They suggest that the evolution of reduced forelimbs was potentially influenced by an upward trend in prey body size. Huge sauropods and other large herbivores may have led to predators evolving stronger skulls and jaws.

Trying to grasp a giant sauropod with relatively small claws may not have been effective. Instead, attacking with powerful jaws and holding onto prey with the mouth could have offered advantages.  As a result, some theropod lineages developed deeper skulls, stronger jaw muscles which increased bite forces.  The researchers described this process as an evolutionary arms race between predators and prey.

The “Tristan” Tyrannosaurus rex specimen shown in anterior view. The robust and powerful skull contrasts with the reduced forelimbs. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

Measuring Skull Strength

For this study, the scientists developed a new method for measuring skull robustness. Several factors were included in their calculations, such as skull shape, bite force, skull compactness and the thickness of skull bones. Compact skulls tend to resist bite force stresses better than long, narrow skulls. On the cranial robusticity scale Tyrannosaurus rex was ranked highest. This helps to answer the question why did T. rex have tiny arms?

Intriguingly, Tyrannotitan (T. chubutensis) a giant carcharodontosaurid from the Early Cretaceous of Argentina was ranked second on the cranial robusticity scale. Tyrannotitan lived more than thirty million years before T. rex. It demonstrates that this trend evolved long before tyrannosaurs dominated North America.

A Tyrannotitan chubutensis scale drawing has been commissioned in preparation for the arrival of the new PNSO Tyrannotitan figure. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

Different Dinosaurs Reduced Their Arms in Different Ways

Although several theropod lineages evolved tiny forelimbs, they did not all shrink them in the same manner. For example, abelisaurids reduced the hands and lower arms dramatically. In contrast, tyrannosaurids reduced the entire forelimb more evenly. This suggests that different developmental pathways produced similar outcomes.

In evolutionary biology, this is another fascinating example of convergent evolution. Different dinosaur groups independently evolved comparable solutions to similar ecological challenges.

The study provides important new insights into theropod evolution. It also helps explain one of the most famous dinosaur features in popular culture. The tiny arms of Tyrannosaurus rex were probably not useless. Instead, they were simply less important as the skull became the primary hunting tool. As theropods evolved increasingly powerful bites, natural selection may have favoured predators that relied more on jaws than claws.

The result was a series of formidable carnivores with massive skulls, bone-crushing bites and surprisingly tiny arms.

An Answer to the Question Why Did T. rex Have Tiny Arms?

This is a fascinating study. Perhaps, the skulls of alvarezsaurid dinosaurs can be examined using this new statistical analysis.  After all, these lightly built theropods had greatly reduced forelimbs too.  This analytical method could also provide a new perspective on avian dinosaurs – birds.

We may have an answer to one of our most often asked questions – why did T. rex have tiny arms?

Everything Dinosaur acknowledges the assistance of a media release from University College London in the compilation of this article.

The scientific paper: “Drivers and mechanisms of convergent forelimb reduction in non-avian theropod dinosaurs” by Charlie Roger Scherer, Elizabeth Steell and Paul Upchurch published in the Proceedings of the Royal Society B.

The award-winning Everything Dinosaur website: Scale Models of Theropods and Other Dinosaurs.

A remarkable new study suggests that Homo erectus populations in East Asia may have co-existed and interbred with Denisovans hundreds of thousands of years ago. The research provides the first molecular evidence linking these ancient human lineages.  This recently published research demonstrates how new protein recovery and analysis techniques can enhance data retrieved in association with hominin fossil discoveries.

The paper, published in the journal “Nature”, analysed fossil teeth from China dating to around 400,000 years ago (Chibanian stage of the Pleistocene Epoch). Scientists extracted ancient proteins preserved inside the dental enamel. As a result, they uncovered genetic clues that may reshape our understanding of human evolution in Asia.

Ancient Proteins from Fossil Teeth

The researchers studied six Homo erectus teeth from three famous Chinese fossil sites. These included Zhoukoudian, the home of “Peking Man”. Zhoukoudian on the North China Plain is now a UNESCO World Heritage site.  The Pliocene and Pleistocene deposits have preserved the remains of early hominins, and the site has been the focus of intense research.

“Peking Man” is thought to represent a sub-species of Homo erectus.  A fossil tooth discovered in 1921 and subsequent hominin fossil discoveries has helped palaeoanthropologists to re-define aspects of hominin evolution. For example, H. erectus is thought to be a direct ancestor of modern humans (H. sapiens).  In addition, whilst it is thought that Homo erectus originated in Africa, it was the first hominin to migrate extensively, with fossil remains found throughout Asia.

Importantly, the team used palaeoproteomics (the study of ancient proteins), rather than ancient DNA analysis. Ancient DNA rarely survives in fossils this old. However, proteins locked within tooth enamel can persist for far longer.

The scientists identified two unusual amino acid variants in a tooth-development protein called ameloblastin. One variant appears unique to East Asian Homo erectus. The second variant proved even more intriguing. Previously, it had only been identified in Denisovans.  The Denisovans are an enigmatic and poorly known archaic hominins that lived in Asia during the middle to late Pleistocene. They are named after the Denisova Cave in the Altai Mountains of Siberia, Russia, where their fossils were first discovered in 2008.

To read an article from 2013 highlighting research into the Denisovans: The Mystery of the Denisovans.

Evidence of Ancient Interbreeding?

The shared protein variant hints that Homo erectus and Denisovans may have interbred in East Asia. If correct, this would add another layer of complexity to the human evolution story. Palaeoanthropologists have long suspected that ancient human species interbred with one another. For example, analysis of other hominin fossil discoveries revealed modern humans interbred with both Neanderthals and Denisovans. Moreover, traces of Denisovan ancestry survive in some living populations today, especially in Southeast Asia and Oceania.

Now, this study suggests that these ancient interactions may have started much earlier than previously thought.

Models depicting three hominins. Homo erectus (left), H. neanderthalensis (centre) and a modern human (H. sapiens) right. The Homo erectus is holding a flaming stick a reference to their tool making abilities and control of fire.

The image (above) shows three figures that help to illustrate hominin evolution.  The Homo erectus figure reflects the control of fire that this species is thought to have possessed.  The models come from an “Evolution of Man” model set produced by Safari Ltd.

To view the range of prehistoric figures including early hominins available: Prehistoric World Figures.

A Complicated Human Family Tree

Scientists know that several human lineages overlapped across Africa and Eurasia during the middle to late Pleistocene. However, their exact relationships remain poorly understood. This new research adds more evidence that ancient humans did not evolve in isolated branches. Instead, different populations probably met and exchanged genes repeatedly.

Interestingly, some researchers now wonder whether certain Chinese fossils traditionally assigned to Homo erectus might actually belong to Denisovan-related groups.

A new species of hominin Homo longi: “Dragon Man” from North-eastern China.

Hominin Fossils Still Hold Molecular Secrets

The study also highlights the growing importance of protein analysis in palaeoanthropology. Recovering DNA from hominin fossil remains extremely difficult. Nevertheless, palaeoproteomics is providing new perspectives on human evolution.  Ancient proteins recovered from hominin teeth may provide evidence to help scientists to better understand human evolution.

As more fossils undergo molecular analysis, researchers may finally untangle the complicated evolutionary history of ancient humans in Asia. Furthermore, how our own species evolved and its complex taxonomic relationship with other hominin taxa.

For now, these ancient teeth provide tantalising evidence that Homo erectus and Denisovans once shared more than just the same landscape. They may also have shared genes.

The scientific paper: “Enamel proteins from six Homo erectus specimens across China” by Qiaomei Fu, Zhongyou Wu, E. Andrew Bennett, Song Xing, Qiang Ji, Zhe Dong, Huiyun Rao, Xuejun Gu, Yizhao Dang, Jun Xing, Kai Zhou and Xiaotian Feng published in the journal Nature.

For scientifically accurate models of ancient hominins and other Pleistocene fauna: Models of Prehistoric Life.