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.

A new genus of sauropod dinosaur has been named from Brazil.  It expands the known diversity of Early Cretaceous sauropods in the northern part of South America. In addition, the newly named dinosaur Dasosaurus tocantinensis provides fresh evidence of dinosaur dispersal between Europe, Africa and South America. The scientific paper describing the new taxon was recently published in the “Journal of Systematic Palaeontology”.

Dasosaurus tocantinensis

The fossil material was discovered by a construction team building a road/rail terminal in the city of Davinópolis, Maranhão state (northeastern Brazil).  The fossils consisted of ten disarticulated caudal vertebrae, limb bones, ribs, a pubis, ischium and several phalanges were found at the bottom of an eight-metre-high slope.  Initially, it was thought these large bones were Quaternary in age.  However, it was soon determined that the material represented a large sauropod dinosaur.

Palaeontologists have confirmed that the fossils (specimen number CPHNAM VT 1600), are from the Aptian-aged strata of the Itapecuru Formation. At an estimated twenty metres in length, Dasosaurus is the largest sauropod to be scientifically described from this formation. Moreover, it is one of the largest dinosaurs known from Brazil.

Dasosaurus has been assigned to the Somphospondyli, a group of titanosauriform sauropods closely related to titanosaurs. Scientists identified several unique anatomical traits in the fossil material. These included unusual ridges on the tail vertebrae and a pronounced lateral bulge on the femur.

A scale drawing of the Brazilian titanosauriform Dasosaurus tocantinensis. Picture credit: Everything Dinosaur (AI assisted).

Picture credit: Everything Dinosaur (AI assisted)

What’s in a Name?

The genus name combines the Greek word “dasos”, meaning forest, with “sauros”, meaning lizard. It is in recognition of this region of Brazil is famous for the remarkable Amazon forest. The species name honours the Tocantins region, close to where the fossils were discovered.

The study highlights an intriguing evolutionary relationship.  Phylogenetic analysis brackets Dasosaurus with the larger, and geologically older Garumbatitan morellensis, a sauropod from the Arcillas de Morella Formation of Spain. As a result, the scientists proposed that the lineage originated in Europe. Subsequently, these dinosaurs dispersed into South America through northern Africa before the Atlantic Ocean fully opened.

This discovery highlights important faunal links between Europe and Gondwana during the Early Cretaceous. In addition, it demonstrates that dinosaur populations could still migrate between landmasses during the Early Cretaceous.

Studying Dinosaur Bone Histology

The research team also examined the microscopic structure of the fossil bones. This branch of palaeontology is known as osteohistology. The scientists identified a mixture of primitive and more advanced traits within the bone tissue. These findings provide valuable information about sauropod growth and development. Moreover, they help scientists understand the evolutionary transition between early neosauropods and later titanosaurs.

The Significance of Dasosaurus tocantinensis

South America has yielded many spectacular sauropod fossils.  For example, some of the largest dinosaurs of all time such as Argentinosaurus and Patagotitan.  However, discoveries of earlier branching titanosauriforms remain relatively rare.

To read about the discovery of the giant titanosaur Patagotitan: A New Giant Dinosaur Gets a Name.

An enormous titanosaur from Brazil Austroposeidon magnificus: Huge Titanosaur from Brazil (Austroposeidon).

Dasosaurus tocantinensis helps fill an important gap in the fossil record. It also expands the known diversity of Brazilian sauropods from the Early Cretaceous. Furthermore, the discovery supports the idea that ancient dinosaur faunas remained interconnected across vast regions. During the Early Cretaceous, Europe, Africa and South America still shared intermittent land connections. These routes allowed dinosaurs and other animals to disperse between continents.

The known dinosaur biota associated with the Itapecuru Formation of Brazil. Picture credit: Everything Dinosaur (AI assisted).

Picture credit: Everything Dinosaur (AI assisted)

With its distinctive anatomy and European affinities, Dasosaurus tocantinensis represents one of the most significant South American sauropod discoveries announced this year.

The scientific paper: “A new titanosauriform with European affinities in the Early Cretaceous of Brazil: insights on Somphospondyli phylogeny, histology and biogeography” by Elver L. Mayer, Julian C. G. Silva Junior, Leonardo R. Kerber, Bruno A. Navarro, Kamila L. N. Bandeira, Juan C. Cisneros, Eliane P. Sousa, Agostina A. Pereira, Manuel A. Medeiros, Rafael M. Lindoso, Francisco Pedro Cavalcanti Neto, Aline M. Ghilardi, Tito Aureliano, Pedro L. Godoy, Gabriel S. Ferreira and Max C. Langer published in the Journal of Systematic Palaeontology.

The multi-award-winning Everything Dinosaur website: Models of Sauropods and Other Prehistoric Animals.

A newly published scientific paper has provided fresh insights into the feeding habits of the famous hadrosaur Maiasaura peeblesorum. Analysis of tooth wear in juvenile Maiasaura compared to adult hadrosaurs suggests that young Maiasaura fed differently from fully grown animals. Researchers examined dental wear associated with Maiasaura peeblesorum fossil teeth.  Dietary insights may help to explain the remarkable success of these ornithischian dinosaurs.

The study focused on the microscopic wear patterns preserved in the dental batteries. Hadrosaurs possessed hundreds of tightly packed teeth. These teeth formed highly efficient grinding surfaces. However, the new research indicates that juveniles used their teeth differently when compared to adult duck-billed dinosaurs.

Haolonggood Maiasaura models. Each adult figure is supplied with a juvenile. The green coloured adult Maiasaura (left) is called Chun Hui. Whereas the model with the tail tinged purple is known as Hua Di. Research suggests that young Maiasaura may have had a different diet compared to the adults.

The image (above) shows the adult and juvenile Maiasaura models available from Haolonggood.  These figures have been praised for their scientific accuracy.

To view the range of Haolonggood figures available: Haolonggood Prehistoric Animal Models.

A Different Diet for Young Hadrosaurs?

The researchers identified different proportions of wear types in juvenile jaws. This evidence suggests that young Maiasaura processed softer vegetation. In contrast, adults probably consumed tougher and more fibrous plants. Consequently, the study supports the idea of an ontogenetic dietary shift. In simple terms, the diet changed as the dinosaur matured. This feeding strategy may have reduced competition between younger and older herd members. Therefore, juveniles and adults could share the same environment whilst exploiting different food resources. In addition, a less fibrous and more nutritious diet could have facilitated rapid growth.  Growing quickly is an effective way to avoid predation.

Duck-billed dinosaurs grew fast to avoid being eaten: Hadrosaurs Grew Fast to Avoid Predation.

The researchers postulated that the more nutritious diet probably consisted of new buds and protein-rich berries.  The extra calories consumed, especially the greater proportion of carbohydrates, fuelled their rapid growth and development.

Maiasaura peeblesorum “Good Mother Lizard”

Maiasaura peeblesorum ranks amongst the most famous dinosaurs discovered in North America. Palaeontologists uncovered extensive nesting colonies in the Upper Cretaceous deposits of Montana. These fossil sites included nests, eggs and juvenile skeletons. As a result, scientists proposed that Maiasaura cared for its young. It was named and scientifically described in 1979 (Horner and Makela). The genus name translates as “good mother lizard”. This duck-billed dinosaur measured around eight to nine metres in length when fully grown.  The jaws analysed in this study came from very young Maiasaura which measured around a metre in length. Maiasaura lived approximately 76 million years ago during the Late Cretaceous (Campanian faunal stage).

“Good Mother Lizard” A Maiasaura and nest. The human silhouette provides a scale. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

Like other hadrosaurs, Maiasaura possessed a broad beak and sophisticated dental batteries adapted for processing plant material. Scientists also think these herbivores lived in large herds.

Studying Tooth Wear

The authors of the study are John P. Hunter (Ohio State University) and Christine M. Janis who is part of the Bristol Palaeobiology Group at the University of Bristol. They analysed wear facets preserved on the teeth. Different types of scratches and polished surfaces can reveal how animals processed their food. Furthermore, these microscopic traces help scientists infer diet and feeding behaviour. The authors concluded that juvenile Maiasaura displayed wear patterns distinct from adults. This difference probably reflects changes in feeding mechanics as the skull and jaws developed.

Understanding Dinosaur Growth and Behaviour

Scientists have studied Maiasaura extensively for decades. Previous research examined growth rates, nesting behaviour and herd structure. This new paper adds another important piece to the puzzle. Moreover, it demonstrates how dinosaur feeding strategies changed throughout life. Studies like this help palaeontologists reconstruct ancient ecosystems more accurately. They also show that dinosaur populations may have divided food resources according to age. Modern animals often display similar ecological separation.  For example, birds with altricial young and an extended nesting period often have different diets depending on their age.  Juveniles grow fast on a more nutritious diet of proteins, sugars and fat compared to the less nutritious diet consumed by the adult.

A Caveat

The researchers highlight that adult dental batteries of Maiasaura were not available for this study. However, as all other saurolophines examined have similarly large proportions of vertical wear on the dental batteries, while lambeosaurines appear to have a greater proportion of horizontal wear, they assume that the dental wear of adult specimens of Maiasaura would resemble that of these related saurolophine taxa.

The paper’s authors acknowledge this to be a weakness in their argument, and that their conclusions would be falsified if the dental batteries of adult Maiasaura were to resemble those of the juveniles. However, the researchers consider that, as with many other cases in paleobiology, it is still worthwhile proceeding with analysis on partial data if there are appropriate caveats placed on the limitations.

Commenting on the significance of this new Maiasaura peeblesorum fossil study, Mike from Everything Dinosaur stated:

“Hadrosaurs dominated many Late Cretaceous ecosystems. Their advanced chewing mechanisms helped them process huge quantities of vegetation. The new Maiasaura peeblesorum fossil teeth study highlights just how adaptable these herbivores may have been”.

The scientific paper: “Tooth wear in juvenile and adult hadrosaurs: implications for parental care in Maiasaura” by John P. Hunter and Christine M. Janis published in Palaeogeography, Palaeoclimatology, Palaeoecology.

The award-winning Everything Dinosaur website: Hadrosaur and Dinosaur Models.