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.

Researchers from Virginia Tech (Virginia, USA) have identified a new species of Late Triassic dinosaur.  The dinosaur has been named Ptychotherates bucculentus.  This new carnivorous dinosaur taxon has been erected based on the detailed examination of an incomplete, well-preserved but jumbled up skull fossil (specimen number CM 31368).  The skull comes from the world-famous Coelophysis Quarry from the Ghost Ranch fossil site in New Mexico. Significantly, the scientists have assigned P. bucculentus to the Herrerasauria.  It might be one of the last surviving members of this earliest-evolving clade of meat-eating dinosaurs.

A New Herrerasaurian Dinosaur

In 1982, a field team from the Carnegie Museum of Natural History (Pittsburgh, Pennsylvania, USA), excavated the fossil from the Coelophysis Quarry. This site contains the preserved remains of numerous vertebrates, but the fossil assemblage is dominated by fossils of the theropod Coelophysis bauri. The fossil bones of over a thousand individuals have been reported. The skull remained in storage and was not studied. However, one of the paper’s authors Sterling Nesbitt (Department of Geosciences, Virginia Tech), arranged for the skull to be scanned using computer tomography (CT). The individual bones were identified and a 3D model of the skull constructed.

When digitally reconstructed the scientists discovered that the jugal bone was unusually tall. Ptychotherates has proportionately the dorsoventrally deepest jugal known for any Triassic-aged dinosaur. Phylogenetic analyses align Ptychotherates bucculentus with Tawa hallae, Chindesaurus bryansmalli and Daemonosaurus chauliodus within the Herrerasauria clade and closely related to the Herrerasauridae family.  The researchers erected the clade Morphoraptora to nest these dinosaurs in.  The Morphoraptora are united by several autapomorphies.  For example, these dinosaurs have extremely fine serrations on their teeth.

Artistic rendition of Ptychotherates bucculentus. Picture credit: Megan Sodano for Virginia Tech.

Picture credit: Megan Sodano for Virginia Tech

The Morphoraptora and Radiohead

Morphoraptora is from the Greek for “form”, “shape” and raptor for “robber”.  This reflects the morphological convergence between members of this clade and theropod dinosaurs.  It loosely translates as “body snatcher” a reference to the close anatomical similarities between the carnivorous Morphoraptora and the Theropoda.  In addition, it honours the 2007 song by the English rock band Radiohead in the album In Rainbows, which one of the authors of the study listened to whilst preparing the manuscript.

The open-access paper was published in the journal Papers in Palaeontology.

To read Everything Dinosaur’s blog post from 2009 about the discovery of Tawa hallae: New Meat-eating Dinosaur from the Chinle Formation.

Our 2011 post about the discovery of Daemonosaurus: The Little “Demon” of Ghost Ranch.

Ptychotherates bucculentus – What’s in a Name?

The skull of Ptychotherates (pronounced Tie-cho-the-rate-ees), was relatively short, but proportionately deep.  Although, no substantial postcranial material is known, scientists estimate that this dinosaur probably measured around 2.2 metres in length.  Like the closely related Tawa, Chindesaurus and Daemonosaurus, it was probably lightly built with the tail comprising around fifty percent of the total body length.

The genus name means “folded jaw hunter”.  This references the carnivorous nature of this dinosaur and also the “folds” and unusual orientations of the fossil material that hampered reconstruction. The species name is from the Latin and translates as “with full cheeks” in reference to the exceptionally tall jugal.

One of the co-authors of the study Simba Srivastava holding the preserved skull of Ptychotherates bucculentus. Picture credit: Spencer Coppage for Virginia Tech.

Picture credit: Spencer Coppage for Virginia Tech

A Late Triassic Hunter

The paper also notes that the phylogenetic relationships of these early saurischian dinosaurs remain controversial. Unfortunately, the fossil material ascribed to Ptychotherates bucculentus, Tawa hallae, Chindesaurus bryansmalli and Daemonosaurus chauliodus does not overlap sufficiently to permit direct fossil comparison. The lack of fossils makes determining the phylogeny difficult. However, the discovery of herrerasaurians in the Coelophysis Quarry establishes that different types of meat-eating dinosaur co-existed during the Late Triassic. Furthermore, the occurrence of morphoraptorans in the Coelophysis Quarry assemblage extends their stratigraphic range later in the Triassic than previously thought.

The exact age of Ptychotherates is hard to determine.  However, it is estimated that this lithe meat-eater lived more recently than 210 million years ago. Ptychotherates bucculentus may have lived shortly before the great extinction event that marked the end of the Triassic. Moreover, scientists have not found any younger herrerasaurian fossils. This discovery suggests that the mass extinction event may have wiped out this dinosaur lineage. In addition, palaeontologists have not found Late Triassic herrerasaurians anywhere else in the world. Therefore, the region that is now southwestern USA may have served as the clade’s final refuge before their extinction.

It had been thought that the end-Triassic extinction wiped out competitors to the Dinosauria.  However, with the discovery of Ptychotherates it suggests that some long-standing dinosaur lineages also died out at this time.

Everything Dinosaur acknowledges the assistance of a media release from Virginia Tech in the compilation of this article.

The scientific paper: “A new taxon of saurischian dinosaur from the Coelophysis Quarry of New Mexico, USA (Triassic: latest Norian or Rhaetian) highlights herrerasaurian diversity in the latest Triassic” by Simba Srivastava and Sterling J. Nesbitt published in Papers in Palaeontology.

The award-winning Everything Dinosaur website: Models of Triassic Dinosaurs and Prehistoric Animals.

A remarkable new sauropod dinosaur discovery is the focus of a recent paper published in the open access journal “PeerJ”.  The study introduces Bicharracosaurus dionidei, fossils of which herald from Upper Jurassic deposits from the Cañadón Calcáreo Formation of southern Argentina. This research captures attention. Not only does it describe a new species, but it also reshapes how scientists understand sauropod evolution in the Southern Hemisphere.

Sauropod Evolution

Much of what we know about sauropod evolution comes from studying fossils from the Northern Hemisphere. Less is known about sauropod evolution and radiation in the Southern Hemisphere. Hence, the discovery of a new sauropod species from southern Argentina is especially significant. In March 2001, farmer Dionide Mesa reported the discovery of some dinosaur vertebrae.  Fieldwork commenced the following year and by 2011 much of the fossil material had been removed.  However, more neck bones (cervical vertebrae) were excavated in 2018.

In total, more than thirty vertebrae, ribs and parts of the pelvis were found.  The material dates from the Upper Jurassic (Oxfordian to Kimmeridgian faunal stages).  Palaeontologists estimate this sauropod fossil material to be approximately 155 million years old.  The fossils probably represent a mature, adult specimen.  Estimates suggest that this dinosaur measured between fifteen to twenty metres in length.

Bicharracosaurus dionidei life reconstruction and scale drawing. Picture credit: Everything Dinosaur (AI assisted).

Picture credit: Everything Dinosaur (AI assisted)

Bicharracosaurus dionidei

What makes Bicharracosaurus dionidei particularly interesting is its unusual mix of sauropod traits. For example, the dorsal vertebrae are similar to the dorsal vertebrae of diplodocids.  However, some fossil bones are reminiscent of the bones of brachiosaurids such as the giant Giraffatitan brancai from the Late Jurassic of Tanzania.  This combination of autapomorphies is unexpected.  Consequently, the research team conducted a detailed phylogenetic analysis.  The results were inconclusive. The overall evidence supports a position of Bicharracosaurus within Macronaria with several analyses and diagnostic characters suggesting brachiosaurid affinities. Bicharracosaurus sits in a somewhat uncertain evolutionary position.

Intriguingly, if the brachiosaurid affinity proves to be correct, then Bicharracosaurus dionidei would be the first member of the Brachiosauridae from the Jurassic of South America.

A Sauropod Puzzle

Several sauropods have been described from fossil material associated with the Cañadón Calcáreo Formation.  For instance, Tehuelchesaurus benitezii which was named and described in 1999 (Rich et al). Tehuelchesaurus is thought to be a macronarian like Bicharracosaurus.  However, whilst Bicharracosaurus shows a combination of sauropod characteristics (diplodocid and brachiosaurid), Tehuelchesaurus is thought to be a member of the Camarasauridae family.

Despite some similarities between Bicharracosaurus and Tehuelchesaurus benitezii fossil material, only in some of the phylogenetic results were these two species recovered as closely related. Whereas in most analyses, Tehuelchesaurus formed a clade with Janenschia robusta, a sauropod from the Late Jurassic of Tanzania. In addition, several diagnostic characters of Bicharracosaurus are absent in Tehuelchesaurus and vice versa. The results also show that other putative macronarian taxa have incongruent positions depending on the dataset.  These inconsistencies are hindering understanding of the early evolution of the Macronaria.

A model of a typical member of the Brachiosauridae family. The Wild Safari Prehistoric World Brachiosaurus dinosaur model. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

The image (above) shows a model of a Brachiosaurus.

For models and replicas of sauropods, including brachiosaurids, diplodocids and other dinosaurs: Dinosaur Models and Dinosaur Toys.

The Naming of Bicharracosaurus dionidei

The taxonomic affinity of this new dinosaur species remains uncertain. It demonstrates that early macronarian evolution was more complicated than previously thought. Until now, scientists relied heavily on fossils from North America and Europe. In contrast, southern continents such as South America and Africa were underrepresented. As a result, evolutionary models may have been biased. Thanks to this newly described sauropod, palaeontologists have the opportunity to test existing ideas and refine theories.  However, it does suggest that sauropod diversity in Gondwana was greater than expected.

The genus name comes from a Spanish term meaning “big animal”. Meanwhile, the species name honours Dionide Mesa, in recognition of the original fossil discovery.

Overall, this study provides fresh insight into one of the most iconic dinosaur groups. It highlights the importance of Southern Hemisphere sauropod fossils. At the same time, it reveals how much there is still to learn. Each new discovery has the potential to challenge established ideas. In this case, Bicharracosaurus dionidei offers a fascinating glimpse into the complex early evolution of macronarian sauropods.

The scientific paper: “Bicharracosaurus dionidei, gen. et sp. nov., a new macronarian (Dinosauria, Sauropoda) from the Late Jurassic Cañadón Calcáreo Formation of Argentina and the problematic early evolution of macronarians” by Alexandra Reutter​, José Luis Carballido, Guillermo José Windholz, Diego Pol and Oliver W.M. Rauhut published in PeerJ.

The multi-award-winning Everything Dinosaur website: Dinosaur and Scientifically Accurate Prehistoric Animal Models.

The discovery of a new titanosaur from Morocco is helping palaeontologists rethink dinosaur diversity at the end of the Mesozoic. Indeed, researchers conclude that Maastrichtian dinosaur diversity is underestimated.  Meet Phosphatotitan khouribgaensis the first definitive titanosaur described from the late Maastrichtian phosphates of Morocco. This exciting discovery provides fresh insights into African dinosaur faunas just before the mass extinction event.

A life reconstruction of the Late Cretaceous Moroccan titanosaur Phosphatotitan khouribgaensis. Picture credit: Everything Dinosaur (AI assisted).

Picture credit: Everything Dinosaur (AI assisted)

Learning About Late Cretaceous African Dinosaurs

The last few million years of the Cretaceous (Maastrichtian faunal stage), saw the final diversification of the Dinosauria prior to the K/Pg extinction event. Discussions of end-Cretaceous dinosaur diversity have focused on well-sampled faunas from Laurasia; far less is known about dinosaurian faunas of the Southern Hemisphere, especially Africa. Subsequently, African dinosaur faunas remain poorly understood.

Fortunately, the Maastrichtian-aged phosphate deposits of Morocco offer a rare window into this ancient palaeoecosystem. The fossils are found in the Khouribga Province (Sidi Chennane locality). They have yielded a variety of dinosaur fossils.  For example, abelisaurids and lambeosaurines.  Titanosaur fossils have been discovered, but no taxon had been erected.  However, the research team which included Dr Nicholas Longrich (University of Bath) were confident enough to describe a new species. Although incomplete, the remains are scientifically significant. The researchers identified dorsal, sacral, and caudal vertebrae, along with parts of the pelvis.  Importantly, the remains although fragmentary, preserve enough anatomical detail to confirm a new genus and species.

To learn more about the remarkable dinosaur biota associated with the Moroccan Maastrichtian phosphate deposits.

To read about Chenanisaurus barbaricus, a giant abelisaurid from North Africa: The Last African Dinosaur?

Two new abelisaurid theropods described: Two Abelisaurs Described from Fragmentary Remains.

Minqaria bata a new duck-billed dinosaur from the Late Cretaceous of Morocco: New Pony-sized Moroccan Lambeosaurine Dinosaur.

Links to South American Giants

Intriguingly, Phosphatotitan shows anatomical similarities with South American titanosaurs. In particular, it shares features with members of the Lognkosauria, a group that includes the enormous, Early Cretaceous Patagotitan (P. mayorum). For example, it possessed short dorsal and caudal centra, expanded dorsal and caudal neural spines, and a broad pubis. This new species differs from titanosaurs described from the Cretaceous of Africa and Europe.

This connection likely dates back to a time before Africa and South America fully separated. Around 100 million years ago, these landmasses split as the South Atlantic Ocean opened. Therefore, Phosphatotitan provides evidence of ancient biogeographic links across Gondwana.  The fossilised bones demonstrate that Phosphatotitan was much smaller than Patagotitan and other South American giants.  Scientists estimate that Phosphatotitan weighed between 3.5 and 4 tonnes. In contrast, Patagotitan is estimated to have weighed around 60 tonnes.

Sue from Everything Dinosaur poses in front of the colossal Patagotitan skeleton which is being exhibited at the Natural History Museum (London). The recently described Phosphatotitan khouribgaensis from the Late Cretaceous of Morocco could be closely related. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

Why was Phosphatotitan khouribgaensis Small?

Despite its titanosaurian heritage and its close taxonomic relationship with Patagotitan, Phosphatotitan was surprisingly modest in size.  Body mass estimates of between three and a half to four tonnes have been proposed.  It was much smaller than most of its South American relatives. Its small size relative to other Lognkosauria suggests a lineage selected for small size. This could be a result of island dwarfism.  During the latest Cretaceous rising sea levels may have isolated parts of Morocco.  Consequently, the smaller landmasses and their limited resources could have favoured smaller dinosaurs.

Alternatively, environmental pressures may have played a key role. In some ecosystems, smaller herbivores outcompete larger ones. This pattern appears in South America, where smaller titanosaurs became more common. Similarly, Egyptian titanosaurs also tend to be small-bodied.  Therefore, Phosphatotitan may reflect a broader trend towards smaller sauropods in certain Late Cretaceous ecosystems.

Phosphatotitan khouribgaensis scale drawing. This titanosaur is thought to weigh around four tonnes and was around nine to ten metres long. Picture credit: Everything Dinosaur (AI assisted).

Picture credit: Everything Dinosaur (AI assisted)

Dinosaur Diversity in the Late Cretaceous May Have Been Underestimated

The discovery of Phosphatotitan khouribgaensis highlights the complexity of Late Cretaceous dinosaur dominated ecosystems. As continents drifted apart, dinosaur populations became increasingly isolated. This isolation led to high levels of endemism. At the same time, occasional dispersal events may have allowed some species to spread between landmasses. Consequently, dinosaur faunas in Gondwana were both diverse and regionally distinct.

The close relationships of Morocco’s titanosaurs and abelisaurids to South American species may reflect a wide distribution of these clades prior to the opening of the South Atlantic and the separation of Africa and South America around a hundred million years ago.  The high endemism seen in both the Northern and Southern Hemispheres suggests that Maastrichtian dinosaur diversity is underestimated.

The scientific paper: “A Titanosaurian Sauropod with South American Affinities (Lognkosauria: Argentinosauridae) from the Late Maastrichtian of Morocco and Evidence for Dinosaur Endemism in Africa” by Nicholas R. Longrich, Agustín Pérez-Moreno, Verónica Díez Díaz, Xabier Pereda-Suberbiola, Nathalie Bardet and Nour-Eddine Jalil published in Diversity.

The award-winning Everything Dinosaur website: Scientifically Accurate Models of Dinosaurs.

An international team of researchers have uncovered evidence that ancient octopuses were once giant, apex predators.  A study involving scientists from Japan and Germany suggests these early cephalopods were at the top of the food chain during the Cretaceous. A Cretaceous giant octopus preying on mosasaurs, plesiosaurs and other vertebrates is a frightening prospect.

The study was published in the journal “Science” earlier this month.  The largest living octopus is the Giant Pacific Octopus (Enteroctopus dofleini).  Its arm span can exceed six metres. However, the octopods revealed in this new research could have reached lengths exceeding nineteen metres (based on mantle size).  Octopi are regarded as highly intelligent and capable hunters.  Subsequently, much larger animals would have been formidable predators and probably competed with marine vertebrates.

Wear on Fossilised Jaws

Octopi and their close relatives have soft bodies.  As a result, they rarely fossilise and the fossil record of octopi is extremely sparse. This makes their evolutionary history difficult to study. For example, we recently published an article that re-examined a famous specimen from the Mazon Creek Lagerstätte.  For years, scientists believed this fossil represented an early octopus named Pohlsepia mazonensis.  However, newly published research revealed evidence of jaws.  Consequently, the fossil most probably represents a decaying nautiloid.

To read more about this research: Oldest Octopus Fossil is Not an Octopus Fossil.

Ironically, it is analysis of super-sized fossilised jaws that has led the researchers to conclude that giant octopi were apex predators in Cretaceous marine environments. These feeding structures preserve far more readily than soft tissues. These jaws, sometimes referred to as beaks, are made of chitin.  It has a greater fossilisation potential than soft tissue.

Using high-resolution grinding tomography and an artificial intelligence model, the team found fossil jaws hidden inside rock samples from Cretaceous deposits spanning 100 to 72 million years ago. These fossils, found in Japan and Vancouver Island, had been well preserved in calm seafloor sediments, retaining fine wear marks that reveal how these animals fed.

A life reconstruction of the Cretaceous giant octopus. Picture credit: Yohei Utsuki, Department of Earth and Planetary Sciences, Hokkaido University.

Picture credit: Yohei Utsuki, Department of Earth and Planetary Sciences, Hokkaido University

Giant Cephalopod Predators of Cretaceous Marine Environments

The fossil jaws have been assigned to two species, following a revision of known Cretaceous specimens.  The two species are:

• • Nanaimoteuthis jeletzkyi
  • Nanaimoteuthis haggarti

The remains have been placed in an extinct group of finned octopi known as Cirrata. By analysing jaw size, shape and wear the team reconstructed their feeding habits. Furthermore, the wear patterns revealed powerful biting forces. The researchers concluded that these animals actively hunted and crushed hard prey. Therefore, they were not passive feeders. Instead, they were powerful predators in the North Pacific Ocean during the age of dinosaurs.

Co-author of the study, Professor Yasuhiro Iba (Hokkaido University) commented:

“Our findings suggest that the earliest octopuses were gigantic predators that occupied the top of the marine food chain in the Cretaceous. Based on exceptionally well-preserved fossil jaws, we show that these animals reached total lengths of up to nearly twenty metres, which may have surpassed the size of large marine reptiles of the same age.”

Evidence of Feeding on Hard Body Parts (Shells and Skeletons)

Careful analysis of the jaws revealed extensive wear.  For example, the team identified scratches, chips and cracking.  These features indicate repeated, forceful biting.  Furthermore, the tips of the beaks were extensively damaged.  Up to ten percent of the jaw tip had been worn away.  The researchers concluded that this damage was not caused by transport induced abrasion.  For example, the remains of the jaws being rolled by water currents along the seabed. The level of damage exceeds that seen in modern cephalopod beaks. As a result, the team inferred an aggressive feeding strategy. Moreover, it suggests these cephalopods regularly tackled hard-bodied prey.

The scientists suggest that cephalopods may have been apex predators in the North Pacific Ocean during the Cretaceous. Picture credit: Everything Dinosaur (AI assisted).

Picture credit: Everything Dinosaur (AI assisted)

The picture (above) shows a hypothesised relationship between predatory vertebrates and the giant Cretaceous octopus.  The mosasaur, plesiosaur and the Xiphactinus figure are from the CollectA range of figures.  Whereas the Cretoxyrhina illustration is based on the PNSO model.

To view the CollectA Prehistoric Life Age of Dinosaurs range: CollectA Prehistoric Life Models.

To view the CollectA Deluxe prehistoric animal models: CollectA Deluxe Prehistoric Animal Figures.

PNSO prehistoric animal figures: PNSO Age of Dinosaurs.

An Intelligent Giant Cretaceous Octopus

Intriguingly, the fossils reveal uneven wear on the jaws.  One side shows more damage than the other side.  This suggests that these octopi might have favoured one side of the jaw when feeding. Asymmetric wear patterns indicate lateralised behaviour, the animal clearly favouring one side of the jaw over the other. Subsequently, the researchers conclude that these octopi were intelligent. In extant animals, lateralised behaviour is linked to advanced brain function.  Therefore, a giant Cretaceous octopus may have displayed complex behaviours.  Perhaps, they were smart enough to catch a plesiosaur.

The Kraken

The mythical Kraken was feared by sailors for centuries. Whilst some extant cephalopods such as the colossal squid (Mesonychoteuthis hamiltoni) can reach lengths of more than ten metres, these Cretaceous giants might have been twice as long.  As a result, during the Cretaceous some invertebrates may have occupied apex predator roles.  This new study proposes that giant octopi may have competed directly with large vertebrate predators. It makes them a rare example of an invertebrate successfully competing with large vertebrate predators.  Furthermore, it provides a tantalising insight into Cretaceous marine environments.

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

The scientific paper: “Earliest octopuses were giant top predators in Cretaceous oceans” by Shin Ikegami, Jörg Mutterlose, Kanta Sugiura, Yusuke Takeda, Mehmet Oguz Derin, Aya Kubota, Kazuki Tainaka, Takahiro Harada, Harufumi Nishida, and Yasuhiro Iba published in the journal Science.