A new species of rinconsaurian titanosaur has been named based on fossils unearthed in northern Patagonia.  The dinosaur has been named Chadititan calvoi. The Rinconsauria clade comprises Late Cretaceous, relatively small and gracile Argentinian titanosaurs. Its composition remains disputed. Phylogenetic analyses reveal contrasting results depending on statistical parameters, but some academics have proposed as many as twenty taxa within this clade.

The fossil material, representing several individuals comes from outcrops of the Anacleto Formation. This formation is thought to have been laid down in the early to middle Campanian faunal stage of the Cretaceous.  The bedding plane associated with these fossils suggests that this dinosaur lived around seventy-eight million years ago.

Chadititan calvoi

The genus name is derived from the local dialect meaning “salt”. The type locality is an extensive salt flat. The species name honours the Argentine palaeontologist Jorge O. Calvo who first proposed the Rinconsauria clade.  Although known from fragmentary remains, palaeontologists have been able to estimate the size of this herbivore.  The partial femora (thigh bones), were compared to more complete Bonatitan (B. reigi) limb bones.  Chadititan is estimated to have been around seven metres long.

A scale drawing of the rinconsaurian titanosaur from northern Patagonia Chadititan calvoi. This dinosaur is estimated to have been about seven metres in length. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

The Rinconsauria was erected in 2007.  The clade consists of slender relatively small titanosaurs with long limbs and modified pelvic girdles.  As far as we at Everything Dinosaur are aware, no osteoderms have been found in association with rinconsaurian fossils.  Dermal armour could have been absent in this clade of titanosaurs.

A Diverse Fossil Assemblage Dominated by Freshwater Turtles

The fossils were found at a location owned by the Marin family near General Roca city (Rio Negro province).  The authors of the scientific paper report a new assemblage of fossils representing a diverse biota.  The site could represent an oasis in what was an exceptionally arid environment.  Gastropods, lungfishes, freshwater turtles and crocodilian fossils have been found.

Turtle fossils are the most common vertebrate fossils present.  They represent over ninety percent of the recovered material.

The scientific paper: “New fossiliferous locality from the Anacleto Formation (Late Cretaceous, Campanian) from northern Patagonia, with the description of a new titanosaur” by Agnolín, Federico L.; Motta, Matías J.; Garcia Marsà, Jordi; Aranciaga-Rolando et al. Paper published – Revista del Museo Argentino de Ciencias Naturales.

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

The direct ancestor of the iconic Tyrannosaurus rex came from Asia. Newly published research lends weight to the theory that the direct ancestor of Tyrannosaurus rex dispersed into North America from Asia via an ancient land bridge. Fossils of T. rex are known from Canada and the USA. However, there is some evidence to suggest that this super-predator may also have roamed what is now Mexico.  The origins of this famous dinosaur, more specifically the Tyrannosaurini, have been hotly debated.

Did the ancestors of T. rex come from Asia or did its ancestors evolve in North America (southern Laramidia)?

The spectacular Titus the T. rex exhibit at Wollaton Hall. A newly published study (May 2025) supports the theory that the ancestors of the iconic Tyrannosaurus rex originated in Asia. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

The Origins of the Iconic Tyrannosaurus rex

Previous studies had suggested that the ancestors of the iconic Tyrannosaurus rex migrated into North America from Asia. This theory was primarily based on the closer taxonomic relationship that T. rex has with Asian tyrannosaurids such as Zhuchengtyrannus and Tarbosaurus. Tyrannosaurus rex was more distantly related to Laramidian tyrannosaurids such as Daspletosaurus and Teratophoneus. So, based on this evidence, it was thought that the lineage of tyrannosaurs that were direct ancestors of the “Tyrant Lizard King” probably evolved in Asia.

Dalman et al in their scientific description of Tyrannosaurus mcraeensis (2024) proposed that the Tyrannosaurus genus evolved in southern Laramidia. Their theory was underpinned by the Late Campanian–Early Maastrichtian age of the T. mcraeensis holotype. However, doubt has been cast over the exact age of the holotype fossil material.

In this new study, a biogeographical analysis of the Tyrannosauridae family, particularly the tribe Tyrannosaurini suggests that tyrannosaurines diversified in the Late Campanian. This diversification supports the idea of a migration of ancestors of T. rex from Asia into North America.

To read Everything Dinosaur’s blog post about Tyrannosaurus mcraeensis: A New Tyrannosaurus Species is Described.

Tyrannosaurus Genus Likely Endemic to North America

The research team conclude that Tyrannosaurus is likely an endemic, North American genus.  The ancestor of the genus dispersed into North American biotas, where it would give rise to Tyrannosaurus. In addition, gigantism occurred numerous times within the Tyrannosauroidea. It was potentially driven by cooler or cooling climates. This study supports the idea that evolutionary changes within the Dinosauria of the Late Cretaceous was partly in response to climate change. The research illustrates the importance of using climate and ecological data to better understand dinosaurian evolution within wider global climatic shifts.

Shedding Light on the Enigmatic Megaraptoridae

The study also sheds light on the evolution of the enigmatic megaraptors.  The Megaraptoridae are a different family of theropod dinosaurs.  How closely related they were to the tyrannosaurs remains disputed.

Some megaraptors were giants.  They occupied the apex predator niche within many ecosystems.  For example, Maip macrothorax from the Late Cretaceous of Argentina may have measured in excess of ten metres long.  Whilst the Tyrannosaurini evolved massive skulls and powerful jaws to take down prey.  Megaraptorids such as Maip evolved in a different direction.  These predators had powerful forelimbs and grasping digits tipped with huge claws.

The new for 2025 CollectA Deluxe M. macrothorax figure shown in lateral view.

The picture (above) shows a 1:40 scale model of Maip macrothorax.  It is part of the CollectA Deluxe range of prehistoric animal figures.

To view the CollectA Deluxe range of models: CollectA Deluxe Prehistoric Animal Models.

Although the extremely fragmentary nature of the megaraptorid was a limiting factor in this research, the team postulate that the megaraptors most likely diverged from the tyrannosaurs around 170 million years ago in Asia.  The megaraptors spread south into what is now Australia, South America and Antarctica via Europe and Africa.

Megaraptorids evolved into the top predators in areas such as Patagonia and Australia, but elsewhere in the world, such as Asia they were replaced by tyrannosaurs.

The scientists would like to extend their modelling but to do so more early tyrannosaur and megaraptor fossils would be needed to make any analysis robust.

The scientific paper: “Rise of the king: Gondwanan origins and evolution of megaraptoran dinosaurs” by Cassius Morrison, Charlie Roger Scherer, Ezekiel V. O’Callaghan, Collin Layton, Colin Boisvert, Mauro Aranciaga Rolando, Leroy Durrant, Pedro Salas, Steven J. R. Allain and Samuel J. L. Gascoigne published by Royal Society Open Science.

For dinosaur toys and figures visit the Everything Dinosaur website: Everything Dinosaur.

Numerous bonebeds associated with horned dinosaurs are known.  For example, the remains of hundreds of Pachyrhinosaurus lakustai have been excavated from a single site in Alberta, Canada. Fossil sites such as this provide evidence that many horned dinosaurs lived in herds. However, until recently there was very little evidence to support the idea of a herd of Triceratops.  That the most famous horned dinosaur “three horned face” formed large, social groups.

To read about the excavation of a Pachyrhinosaurus skull from a bonebed: Remarkable Horned Dinosaur Skull Excavated from Bonebed.

Researchers from the Naturalis Biodiversity Centre (Leiden, Netherlands) have helped to change our view of Triceratops.  They have identified the remains of a least five individuals that lived and died together.  A decade of careful study of a dinosaur bonebed discovered in Wyoming has revealed that Triceratops too moved around in groups.

An artist’s reconstruction of a herd of Triceratops dinosaurs. Picture credit: Bart Bus.

Picture credit: Bart Bus

A Fossil Site Reviews a Herd of Triceratops

Ironically, the field team set out to find a T. rex. Nonetheless, what they found in the summer of 2013 has proved to be of much greater value to science than a single theropod specimen.  The research work at the Lance Formation (Maastrichtian) exposures has revealed a large bonebed of Triceratops (T. horridus). Over the last decade, some twelve hundred individual bones have been excavated from the site. Importantly, the abundant postcranial material displays features of both subadult and adults. This fossil locality can shed new light on the ontogeny and possible gregarious behaviour of this iconic dinosaur.

Field team member Jimmy de Rooij digging up a Triceratops fossil. Picture credit: Marten van Dijl (Naturalis Biodiversity Centre).

Picture credit: Marten van Dijl (Naturalis Biodiversity Centre)

A team of palaeontologists and volunteers spent many summers at the site mapping and extracting the precious bones.  One of the researchers Jimmy de Rooij hopes to receive a PhD from Utrecht University for his work on this remarkable bonebed.

He commented:

“The material is of very god quality.  This enabled us to show that these Triceratops grew really slowly for instance.”

It is thought that all these dinosaurs perished together, perhaps mired in a swamp.  The fossils are all contained in a thin layer, without the bones of other species present.

Jimmy de Rooij holding a Triceratops horn. Picture credit: Naturalis Biodiversity Centre.

Picture credit: Naturalis Biodiversity Centre

Publishing Scientific Papers and Opening an Exhibition

A scientific paper outlining the fossil discoveries and postulating that this was strong evidence to indicate that Triceratops horridus was gregarious was published in 2019.  However, the research into this treasure trove of horned dinosaur bones continues today.  An exhibition telling the story of the Wyoming bonebed and its significance to palaeontology has opened at the Naturalis Biodiversity Centre.

A sixth Triceratops specimen on display at the Naturalis Biodiversity Centre. Picture credit: Naturalis Biodiversity Centre.

Picture credit: Naturalis Biodiversity Centre

Study of the physical and chemical properties of hundreds of individual bones indicates that Triceratops migrated.  All five Triceratops specimens exhibit the same characteristics.  In other words, this iconic dinosaur species moved around in groups, at least for part of the time.  Visitors to Wyoming at the end of the Cretaceous might have spotted a herd of Triceratops!

A Herd of Triceratops horridus

The CollectA T. horridus ceratopsian figure in right lateral view. This Triceratops dinosaur model has an articulated lower jaw. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

The image (above) shows a 1:40 scale model of Triceratops horridus.  This is the biggest Triceratops species described to date and one of the largest ceratopsids known to science.  The replica is from the CollectA Deluxe range of scale prehistoric animal figures.

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

The discovery of what potentially could be a small herd of Triceratops poses some intriguingly questions.  For example, did these herbivores indulge in complex social behaviours?

Professor Anne Schulp (Naturalis Biodiversity Centre/Utrecht University), and De Rooij’s PhD supervisor proudly stated:

“Naturalis, the national natural history museum of the Netherlands, now has the biggest Triceratops find in the world, and Utrecht University has the first Dr Triceratops in the Netherlands. De Rooij’s work didn’t just result in research papers, but also in an exhibition about his findings.”

Mike from Everything Dinosaur commented:

“The exhibition will give dinosaur fans young and old the chance to learn more about Triceratops.  Indeed, visitors will be able to see the five fossil Triceratops specimens together some sixty-seven million years after they lived and died together.”

Visit the Everything Dinosaur website, which is award-winning and customer-friendly: Dinosaur Models and Prehistoric Animal Figures.

Everything Dinosaur acknowledges the assistance of a media release from the Naturalis Biodiversity Centre in the compilation of this article.

Phytosaurs were a geographically widespread group of semiaquatic reptiles that thrived in the Late Triassic. Everything Dinosaur team members look at the remarkable phytosaur Colossosuchus techniensis and other related genera.

The phylogenetic position of the phytosaurs remains disputed. This is in part as little is known about their ancestral forms. For example, some scientists classify phytosaurs as members of the Archosauria, uniting them in the same clade as crocodiles, pterosaurs, dinosaurs and birds. However, other researchers, notably the American palaeontologist Sterling Nesbitt does not define the Phytosauria as archosaurs, but as close relatives to the Archosauria (Archosauriformes).

Often depicted with a sprawling gait, a trackway assigned to a phytosaur (Apatopus) indicates that these reptiles adopted a “high walk” gait.  They had an erect stance, albeit with a tail drag, and a parasagittal gait, much as crocodiles do today.

Phytosaurs Resembled Extant Crocodilians

These animals superficially resembled crocodilians, although they were not closely related to modern crocodiles. This is an example of convergent evolution.  Convergent evolution is the process through which distantly related or unrelated organisms evolve similar characteristics or adaptations in response to similar environmental pressures.  For instance, most phytosaurs were probably aquatic ambush predators.  They occupied an environmental niche in ancient ecosystems similar to the niche occupied by extant crocodilians.

A museum exhibit featuring a typical phytosaur. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

Characteristics of Phytosaurs

Although superficially resembling crocodiles there were notable differences.  For example, the nostrils of phytosaurs were located high up on the skull, almost between the eyes. The nostrils were located atop a dome-like structure towards the posterior of the snout. In crocodilians, the nostrils are located at the tip of their long snouts.

The location of the nostrils in a phytosaur. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

In addition, phytosaurs lacked the bony secondary palate found in crocodilians.  Although, they probably possessed a fleshy secondary palate that enabled them to breathe whilst they had water in their mouths.  Unfortunately, the presumed presence of a fleshy palate is not confirmed in the fossil record, probably due to this structure’s poor preservation potential.

The arrangement of dermal armour was probably different too. Phytosaurs probably had a paired row of armoured scutes running down their backs. In contrast, crocodilians have multiple rows of scutes.

The manus (hand) of these reptiles such as the phytosaur Colossosuchus techniensis consisted of five digits.

A description of the phytosaur manus:

• The manus is short and rounded with digit III being longest.
• Digits II and IV are approximately the same length.
• Moreover, digit V is the smallest digit. Digit I (pollex) is short but robust.
• Claws are present on digits I to IV.
• The largest claws being located on digit I and II.

A description of the phytosaur pes:

• The pes had five digits.
• Digit I was short and quite robust.
• Digits II, III and IV were long and slender.
• Digit IV was the longest.
• It is believed that all the digits had claws.
• Digit V was much reduced and the shortest digit. It did have a small claw.

How Big were the Largest Phytosaurs?

Scientists remain uncertain over the size of the largest taxa.  Some phytosaurs may have been bigger than the largest living crocodilian the Saltwater crocodile (Crocodylus porosus) which rarely exceeds six metres in length. For example, Rutiodon carolinensis from the southeastern United States is thought to have measured about eight metres long.  It is known from numerous fossil specimens including skull material. The largest skull measures seventy-seven cm in length.

Furthermore, Smilosuchus gregorii is thought to have reached a length of around eight metres.  Some body length estimates for this species exceed twelve metres. However, these estimates are based on highly fragmentary specimens. The recently described Indian phytosaur Colossosuchus techniensis is also estimated to have reached a length of around eight metres.

The 2023 scientific paper describing the phytosaur Colossosuchus techniensis:

“A giant phytosaur (Diapsida, Archosauria) from the Upper Triassic of India with new insights on phytosaur migration, endemism and extinction” by Debajit Datta and Sanghamitra Ray published in Papers in Palaeontology.

Mike from Everything Dinosaur commented:

“Intriguingly, there are numerous examples of at least two phytosaur species being coeval.  One species is often narrow-snouted [Dolichorostral] with teeth that are very similar.  The second species often has a much more robust snout [Brachyrostral] with differently shaped teeth.  Often the robust snouted forms have long fangs at the end of their jaws.  This suggests that these two phytosaurs evolved to take advantage of different food resources although they shared the same environment. Niche partitioning seems to have taken place quite frequently within the Phytosauria.”

Visit the Everything Dinosaur website: Prehistoric Animal Figures.

Palaeontologists explain this niche partitioning phenomena by suggesting that the ancestral phytosaur species specialised in eating different things.  They eventually diverged into two closely related but different species. It is remarkable that this evolutionary pattern is repeated so often within the Phytosauria fossil record.

Time to catch up on this year’s dinosaur discoveries.  For instance, a new species of North African carcharodontosaurid was described recently.  The fragmentary fossil material representing Tameryraptor markgrafi was excavated during the expedition to Egypt led by the famous German palaeontologist Ernst Stromer von Reichenbach.  The naming of this new dinosaur (Kellermann, Cuesta and Rauhut), demonstrates that the theropods of the Bahariya Oasis and the Moroccan Kem Kem Group are not as closely related as previously thought.  Researchers have stated that the proposed faunal similarities between these two strata need further examination.

Tameryraptor markgrafi

The partial skeleton from the Egyptian Bahariya Oasis, found in April 1914, consisted of elements from the skull, a partial dorsal vertebra, upper limb ones, the proximal end of the pubis and part of a caudal vertebra.  It was described by Stromer in 1931.  The material was first assigned to the species Megalosaurus saharicus, which had been described from isolated teeth found in geologically older rocks in Algeria. Unfortunately, almost all of the material from the Bahariya Oasis, including these fossils was destroyed during a bombing raid in World War II.

A detailed reassessment of the available information on the Egyptian carcharodontosaurid, including a previously undescribed photograph of the exhibited specimen, revealed that it differed from the Moroccan Carcharodontosaurus saharicus in several ways.  It also possessed a horn-like rugosity on the nasal bone.  These unique characteristics permitted the research team to confidently reassign these fossils, removing them from the C. saharicus taxon and allowing the naming of a new species of North African theropod.

A photograph of the holotype fossil material (SNSB-BSPG 1922 X46) on display. This photograph was taken prior to April 1944. Picture credit: Kellermann et al.

Picture credit: Kellermann et al

The fossils were discovered around two kilometres from Ain Gedid on the Western foot of the Gebel Harra in basal layers of hardened, gypsum-free marl.  The fossil material it thought to be around ninety-five million years old (Cenomanian faunal stage of the Late Cretaceous).

Based on the photographic evidence and a single endocast of the skull that remains, palaeontologists have estimated that Tameryraptor was around ten metres long.

An illustration of the large carcharodontosaurid from the Bahariya Formation (Egypt). It has been named Tameryraptor markgrafi. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

The Etymology of Tameryraptor

The genus name is derived from one of the more informal names for Egypt (ta-mery), which means beloved land and the Latin word for thief (raptor).  The species name honours Austrian fossil collector Richard Markgraf, who discovered most of the dinosaur remains described by Ernst Stromer von Reichenbach.

The scientific paper: “Re-evaluation of the Bahariya Formation carcharodontosaurid (Dinosauria: Theropoda) and its implications for allosauroid phylogeny” by Maximillian Kellerman, Elena Cuesta and Oliver W. M. Rauhut published in PLOS One.

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

An American biotech firm has claimed that their gene editing techniques has led to dire wolf de-extinction.  The front cover of the prestigious “Time” magazine features a remarkable photograph of an oversized wolf staring back at the camera.  It is a powerful image, a testament to advances in gene manipulation and editing undertaken by Colossal Biosciences. However, the young wolves named Romulus, Remus along with a younger female named Khaleesi are not Aenocyon dirus.

A photograph of the two males (Romulus and Remus) aged three months. These canids born 10/1/2024 Picture credit: Colossal Biosciences.

Picture credit: Colossal Biosciences (media release received 08/04/2025)

Dire Wolf De-extinction

Early this month, Colossal Biosciences announced the rebirth of the once extinct dire wolf (A. dirus). It was claimed this was the world’s first successfully de-extincted animal.

Commenting on the company’s work CEO Ben Lamm stated:

” I could not be more proud of the team.  This massive milestone is the first of many coming examples demonstrating that our end-to-end de-extinction technology stack works.”

He added:

“Our team took DNA from a 13,000-year-old tooth and a 72,000-year-old skull and made healthy dire wolf puppies. It was once said, any sufficiently advanced technology is indistinguishable from magic. Today, our team gets to unveil some of the magic they are working on and its broader impact on conservation.”

Dr Beth Shapiro (Chief Science Officer) explained that the company’s novel approach to improving an ancient genome in the absence of more complete material set a new standard in gene management.

Team members at Everything Dinosaur first came across Dr Shapiro’s research a decade ago.  Dr Shapiro had written an intriguing book outlining how modern science and gene manipulation could result in the de-extinction of the Woolly Mammoth.

Everything Dinosaur’s review of “How to Clone a Mammoth”: How to Clone a Mammoth (De-extinction).

Dr Shapiro commented:

“Together with improved approaches to recover ancient DNA, these computational advances allowed us to resolve the evolutionary history of dire wolves and establish the genomic foundation for de-extinction – specifically for selecting with confidence dire wolf specific genetic variants that establish our targets for gene editing.”

Challenging the De-extinction of Aenocyon dirus

Whilst the birth of these canids represents a considerable achievement.  Many scientists have cast doubts on the claim that these three animals represent a revival of a long extinct taxon.  The idea that the dire wolf has been resurrected has been challenged.  Extinction remains permanent.  Instead, the scientists at Colossal Biosciences have used synthetic biology technologies to identify in ancient DNA from dire wolf remains key segments of the genetic code that could be manipulated to produce a modified grey wolf (Canis lupus).

In essence, what has been produced is a grey wolf but with some dire wolf-like traits, such as the larger skull and white fur.

The Rebor dire wolf/fantasy figure with its product packaging. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

The picture (above) shows a replica of a dire wolf.  It is part of the Rebor range of models and figures.  There has been a renewed interest in dire wolves since they featured in the hit fantasy television series “Game of Thrones”.

To view the range of Rebor figures in stock: Rebor Figures and Models.

Implications for Conservation

The research may have important applications in helping to maintain healthy populations of highly endangered animals. For example, Colossal Biosciences have also produced two litters of red wolves from three different genetic founder lines. The red wolf (Canis rufus) is the most critically endangered wolf in the world.  These litters include one adolescent female red wolf (Hope) and three male red wolf puppies (Blaze, Cinder, and Ash).

Mike from Everything Dinosaur said:

“They are beautiful animals, and they represent an example of the huge advances being made in biosciences.  However, numerous academics and scientists have stated that they are not dire wolves but essentially a modified grey wolf that has some physical traits that represent a different species”.

Colossal Biosciences are continuing to research the de-extinction of other iconic animals.  For example, they are examining the possibility of resurrecting the Thylacine.  In addition, CEO Ben Lamm has claimed that the first Woolly Mammoth calves produced using this type of technology might be born within three years.

Resurrecting the Woolly Mammoth: The Return of the Woolly Mammoth.

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

Scientists have named a unique, two-fingered therizinosaur species.  The fossils of Duonychus tsogtbaatari come from the Upper Cretaceous Bayanshiree Formation of the Gobi Desert (Mongolia).  This is the first time that a reduction of the digits on the manus has been recorded within the Therizinosauridae family.  All other therizinosaurs possessed three fingers on each hand.  Moreover, each finger ended in a curved claw.  Some of the claws of therizinosaurs were huge.  For example, one of the largest, Therizinosaurus cheloniformis had finger claws over a metre in length.

A life reconstruction of Duonychus tsogtbaatari. This dinosaur had two fingers on each hand. Although the fossils from which this new species has been described represent a subadult. Scientists have calculated that It weighed approximately 260 kilograms and was around three metres in length. Picture credit: Tim Bollinger.

Picture credit: Tim Bollinger

Duonychus tsogtbaatari

Duonychus (pronounced due-oh-ny-kus) translates from the Greek as “two claws”.  The species name honours the Mongolian palaeontologist Khishigjav Tsogtbaatar.  The discovery of this therizinosaur is doubly unique.  One of the sheaths on a fossil claw (digit I) has been preserved.  The sheath made from the protein keratin (same as our hair and fingernails), reveals that the claw was much longer than the underlying bone.  It was forty percent longer than the claw’s bony core.  It is the largest claw of its kind found fully preserved in this way.  The total claw length has been estimated at around thirty centimetres.

Duonychus tsogtbaatari was not carnivorous.  These long claws were probably not used to attack other dinosaurs.  Although, they could have had a defensive function or have been used in intraspecific combat.  The researchers studying the fossil material believe the long, curved claws and the ability of Duonychus to flex them would have helped this animal to grasp vegetation.

Duonychus tsogtbaatari data card. Picture credit: Tim Bollinger.

Picture credit: Tim Bollinger

Digit Reduction in Theropod Dinosaurs

The most famous two-fingered theropod dinosaur is Tyrannosaurus rex.  Duonychus is not closely related to T. rex.  However, both these dinosaurs evolved from ancestors that had three digits on each hand.  So, why did some theropod dinosaurs lose digits?  It is likely that the outer fingers of the hand became less useful and so they were gradually reduced over the time.  An evolutionary pathway led to the outer fingers becoming redundant, then vestigial, before finally disappearing altogether. Alternatively, digits I and II became increasingly dominant and thus enlarged.  This led to the eventual reduction and elimination of digit III.

Intriguingly, the hand claws of Duonychus were highly curved.  The researchers conclude that the extremely curved claws were adaptations to help this animal to “hook” branches and pull them within easy reach.  In essence, the reduction of digits was an evolutionary adaptation towards more efficient feeding.

Potential Niche Partitioning?

The sediments of the Bayanshiree Formation preserve a diverse dinosaur biota.  For example, there were at least three other therizinosaurs that were likely coeval with Duonychus.  All the other Bayanshiree Formation therizinosaurs described to date had three fingers on each hand.  With so many therizinosaurs in the same environment, it is possible that Duonychus evolved reduced digits to permit it to feed on different types of vegetation.  The reduced fingers could represent evidence of niche partitioning within the Therizinosauridae associated with these strata.

The four therizinosaurs described from the Bayanshiree Formation to date:

• Segnosaurus (S. galbinensis) named in 1979. One of the largest therizinosaurs known with a length of around seven metres.
• Erlikosaurus (E. andrewsi) named in 1980.  Measuring around three and half metres in length it had a robust beak suggesting a diet of mainly vegetation.
• Enigmosaurus (E. mongoliensis) named in 1983.  Some scientists consider Enigmosaurus a junior synonym of Erlikosaurus.  Although, the discovery of Duonychus lends support to the idea that several different types of therizinosaur were present.
• Duonychus (D. tsogtbaatari) named in 2025.  The first didactyl therizinosaur, possessing only two manual digits. In addition, the keratinous sheath on digit I provides a rare insight into theropod claw structure.

It is also worth noting that several other potential therizinosaur fossil specimens have been excavated from the Bayanshiree Formation.  These have yet to be formally named and described.

Our thanks to Tim Bollinger for permission to use his Duonychus illustrations in the compilation of this article.

Take a look at Tim Bollinger’s work under the moniker UnexpectedDinoLesson:

Instagram – @unexpecteddinolesson
Facebook – @UnexpectedDinoLesson
X (Twitter) – @Dino_Lesson

The scientific paper: “Didactyl therizinosaur with a preserved keratinous claw from the Late Cretaceous of Mongolia” by Yoshitsugu Kobayashi, Darla K. Zelenitsky, Anthony R. Fiorillo and Tsogtbaatar Chinzorig published in the journey iScience.

A fragment of a left femur found in the Atlas Mountains of Morocco is the earliest evidence of the cerapodan clade of dinosaurs.  An open access study, published in the Royal Society Open Science earlier this month posits that this fragmentary specimen is the world’s oldest cerapodan fossil. As such, it is helping palaeontologists to understand the evolutionary origins of one of the most diverse and successful dinosaur groups.

The World’s Oldest Cerapodan

The Cerapoda consists of bird-hipped dinosaurs (part of the Ornithischia). These mainly herbivorous dinosaurs became a major component of Cretaceous terrestrial ecosystems. They dominated the herbivorous niche in Late Cretaceous ecosystems in the Northern Hemisphere. One of the secrets of their evolutionary success is that they evolved sophisticated chewing mechanisms to help them break down plant material. Early cerapodans were small and bipedal. However, by the Late Cretaceous they had evolved obligate quadrupedality and some of these dinosaurs were the largest non-sauropod dinosaurs on Earth.

The term Cerapoda is a combination of the words ceratopsian and ornithopod.

A cerapodan dinosaur skeleton on display.  This is a cast of the enormous duck-billed dinosaur (Edmontosaurus annectens). Hadrosaurs like Edmontosaurus were a major component of Late Cretaceous ecosystems in North America. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

The Remarkable El Mers III Formation

The fossil was discovered in 2020 by a field team exploring exposures of the El Mers III Formation at Boulahfa, near Boulemane, central Morocco.  The strata were laid down during the Bathonian of the Middle Jurassic (168 to 165 million years ago). This specimen represents the world’s oldest cerapodan. The El Mers III Formation has also yielded the world’s oldest ankylosaur, the first discovered in Africa (Spicomellus afer), as well as one of the oldest stegosaurs.  For example, in 2019 we wrote a blog post about Adratiklit boulahfa, the first stegosaur to be described from North Africa.

To read our blog post about Spicomellus afer: The Earliest Ankylosaur Known to Science and Africa’s First.

Our 2019 article about A. boulahfa: North Africa’s First Stegosaur.

These North African deposits are providing evidence of some of the earliest members of key clades within the Dinosauria.  The fossil (specimen number USMBA 001) consists of a femoral head offset on a distinct neck with a constriction between the head and the trochanter (a ridge that indicates a large muscle attachment).  These anatomical characteristics identify the fossil as coming from a cerapodan dinosaur.

USMBA 001, proximal left femur of a cerapodan dinosaur in (A) anterior, posterior (B) and (C) proximal (dorsal). Lateral view (D) and (E) medial view. Note the key – ar, ridge on the anterior surface; gt, greater trochanter; hd, head; ls, ligament sulcus; tr, trough separating head from greater trochanter; u, u-shaped sulcus; ur, ridges bordering u-shaped sulcus. Scale bar equals 2 cm. Picture credit: Maidment et al (Royal Society Open Science).

Picture credit: Maidment et al (Royal Society Open Science)

The researchers conclude that further sampling of the El Mers III Formation sediments will be crucial in helping to understand the radiation of ornithischian dinosaurs. The research team hope to find more fossil material representing the world’s oldest cerapodan.

Callovosaurus leedsi and a Scottish Fossil

Previously, the oldest definite cerapodan fossil was a partial left femur from the Oxford Clay Formation found at Fletton, near Peterborough, Cambridgeshire. The type species was described by the English naturalist Richard Lydekker in 1889. Originally named Camptosaurus leedsi this dinosaur was redescribed in 1980 (Galton) and renamed Callovosaurus leedsi. Its taxonomy has yet to be resolved. The fossil specimen number NHMUK R1993, could represent a basal iguanodontian or perhaps a dryosaurid.

A fragmentary fossil of an ornithopod (Callovosaurus leedsi). Previously, this fossil represented the oldest cerapodan described to date.

Picture credit: Dean Lomax

The fossil is thought to be approximately 164 million years old.

Rounded, tridactyl footprints from bipedal dinosaurs which are thought to represent cerapodan dinosaurs have been reported from Middle Jurassic sediments from around the world. However, early cerapodan body fossils are exceptionally rare.  A partial dinosaur skeleton from the Isle of Skye, could be another cerapodan.  This specimen is around 166 million years old.  Unfortunately, whilst likely to represent a dinosaur, these fossils are too poorly preserved and fragmentary to definitely identify this material as a representative of the Cerapoda.

To read Everything Dinosaur’s article about the Isle of Skye fossil specimen: Rare Elgol Dinosaur Fossil Scientifically Described.

Defining the Cerapoda

The Cerapoda is a clade within the Ornithischia (bird-hipped dinosaurs). It consists of two distinct subgroups, the Ornithopoda and the Marginocephalia. The clade is extremely diverse.  The ornithopods include iconic dinosaurs such as Iguanodon, Hypsilophodon and the Hadrosauriformes. In turn, the Marginocephalia comprises the horned dinosaurs (Ceratopsia) and the bone-headed dinosaurs (pachycephalosaurs).

The scientific paper: “The world’s oldest cerapodan ornithischian dinosaur from the Middle Jurassic of Morocco” by Susannah Maidment, Driss Ouarhache, Richard J Butler, Khadija Boumir, Ahmed Oussou, Kawtar Ech-charay, Abdessalam El Khanchoufi and Paul M Barrett published in Royal Society Open Science.

Visit the Everything Dinosaur website: Dinosaur and Prehistoric Animal Models.

Recently published temnospondyl research suggests that adopting a generalist feeding ecology helped these ancient amphibians to survive the end-Permian mass extinction event.  The study published this week in the journal “Royal Society Open Science”, concludes temnospondyl’s success lay in their generalist feeding ecology. The temnospondyls consist of an extinct clade comprising around three hundred known species.  They evolved in the Early Carboniferous and persisted until the Early Cretaceous.  This represents a timespan of around two hundred and thirty million years.  Temnospondyls were traditionally classified as amphibians, although their taxonomic affinity with the Amphibia remains controversial.  It is more technically correct to refer to these vertebrates as anamniote tetrapods.

A dorsal view of the CollectA Deluxe Koolasuchus a late surviving temnospondyl from the Early Cretaceous of Australia. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

The photograph (above) shows a dorsal view of Koolasuchus cleelandi model. It is the youngest temnospondyl described to date.  Fragmentary fossils are thought to be around 125-120 million years old (Barremian – Aptian faunal stages of the Cretaceous).  The model is from the CollectA Deluxe range of scale prehistoric animal figures.

To view this range of prehistoric animal models: CollectA Deluxe Prehistoric Life Models.

A Mystery of the end-Permian Mass Extinction Event

One of the mysteries of the end-Permian mass extinction was the subsequent success of temnospondyls. This catastrophic global event occurred approximately 252 million years ago.  It was the largest extinction event in the Phanerozoic, marked by the loss of as many as 90% of all species.  Although many types of temnospondyl died out, following this mass extinction temnospondyls diversified rapidly during the Early Triassic.  Numerous lineages arose.  These lineages continued, although with diminishing diversity throughout the remainder of the Triassic.  A few taxa survived into the Jurassic before the temnospondyls are thought to have finally become extinct during the Early Cretaceous.

Researchers led by scientists from the University of Bristol propose that these animals thrived after the mass extinction event by feeding on freshwater prey that evaded terrestrial predators.

By adopting a generalist feeding ecology, these predators could consume a wide variety of prey despite all the environmental changes going on during the Triassic. A broader examination of Triassic ecosystems also indicates that the freshwater habitats temnospondyls preferred provided them with a relatively stable variety of food resources.  This allowed them to thrive while strictly terrestrial predators made do with meagre, unstable resource availability on land.

A Mastodonsaurus rises out of the depths to ambush a small, archiosauriform (Jaxtasuchus). Picture credit: Mark Witton.

Picture credit: Mark Witton

Mastodonsaurus (see image above), is known from the Middle Triassic of Europe.  It was one of the largest temnospondyls, with an estimated body length of more than five metres.

Lead author of the study Aamir Mehmood (University of Bristol School of Biological Sciences), commented:

“One of the great mysteries has been the survival and flourishing of a major group of amphibians called the temnospondyls.  These were predatory animals that fed on fishes and other prey, but were primarily linked to the water, just like modern amphibians such as frogs and salamanders. We know that climates then were hot, and especially so after the extinction event. How could these water-loving animals have been so successful?”

The Triassic “Tropical Dead Zone”

The Early Triassic was a time of repeated volcanic activity leading to long phases of global warming, aridification, reductions in atmospheric oxygen, acid rain and widespread wildfires, creating conditions so hostile that the tropics became devoid of animal life. This “tropical dead zone” drastically impacted the distributions of both marine and terrestrial organisms.

Co-author Dr Suresh Singh said:

“We collected data on a hundred temnospondyls that lived throughout the Triassic and wanted to look at how their ecologies changed. We measured their body sizes and features of the skulls and teeth that tell us about function.”

Dr Armin Elsler another co-author of the temnospondyl research paper added:

“Much to our surprise, we found that they did not change much through the crisis. The temnospondyls showed the same range of body sizes as in the Permian, some of them small and feeding on insects, and others larger. These larger forms included long-snouted animals that trapped fishes and broad-snouted generalist feeders. What was unusual though was how their diversity of body sizes and functional variety expanded about five million years after the crisis and then dropped back.”

Due to the intense global warming of the first five million years of the Triassic, there is evidence that life on land and in the sea moved away from the tropics to avoid the heat.

Professor Mike Benton (University of Bristol) explained:

“Our work shows that the temnospondyls, unexpectedly, were able to cross the tropical dead zone. Fossils are known from South Africa and Australia in the south, as well as North America, Europe and Russia in the north. The temnospondyls must have been able to criss-cross the tropical zone during cooler episodes.”

An exhibit featuring a reconstruction of the skeleton of the giant Permian temnospondyl Eyrops. New research suggests that temnospondyl’s success during the Early Triassic lay in their generalist feeding ecology. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

The Decline of the Temnospondyls

Aamir summarised the team’s findings stating:

“Their burst of success in the Early Triassic was not followed up. They coped with the hot conditions probably by having a low requirement for food, by being able to eat most prey animals, and by hiding in sparse water bodies. But when the ancestors of dinosaurs and of mammals began to diversify in the Middle Triassic, the temnospondyls began their long decline.”

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

The scientific paper: “The ecology and geography of temnospondyl recovery after the Permian – Triassic mass extinction” by Aamir Mehmood, Dr Suresh Singh, Dr Armin Elsler and Professor Michael Benton published in Royal Society Open Science.

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

A jumbled set of bones first spotted on a beach on the southern portion of the Isle of Skye in 1973 have been identified as a probable ornithopod.  The Elgol dinosaur fossil is Scotland’s earliest recorded dinosaur fossil discovery.  A research team led by Dr Elsa Panciroli (NERC Independent Research Fellow at National Museums Scotland), visited the site in 2018 and began the challenging process of extracting the fossil specimen from the surrounding boulders.

A specialist Canadian company was invited to supervise the extraction of the rare fossil.  Once the difficult task of releasing the fossil slab was completed, it was carefully loaded onto an inflatable dingy and piloted safely back to port by a local crew from Elgol’s Bella Jane Boat Trips.  The researchers were so worried about the fossil block sinking that they tied several buoys to it in the hope that if the boat should capsize, the rare fossil could still be located.

Lead author Dr Elsa Panciroli with the Elgol dinosaur fossil. The jumbled bones have proved difficult to identify. Picture credit: Neil Hanna.

Picture credit: Neil Hanna

The Dinosaur Fossil Record of Scotland

The fossil record of dinosaurs in Scotland mostly comprises isolated highly fragmentary bones from the Great Estuarine Group in the Inner Hebrides.  These sediments were deposited in the Middle Jurassic (Bajocian–Bathonian faunal stage).  The Elgol dinosaur fossil is estimated to be around 166 million years old. It is the first and most complete partial dinosaur skeleton currently known from Scotland. The material has been assigned a specimen number (NMS G.2023.19.1).

After manual preparation, the scientists were able to identify part of the spine, ribs and elements from the hips (a partial ilium).  Unfortunately, micro-CT scanning failed to help with fossil identification.  However, the team are confident that the material does represent a dinosaur, an ornithischian and most likely an ornithopod.  If it does prove to be an ornithopod, then it would be one of the world’s oldest ornithopod body fossils described to date.

The Elgol dinosaur fossil has been interpreted to represent an early ornithopod. Picture credit: Maija Karala.

Picture credit: Maija Karala

Lead author of the study, Dr Elsa Panciroli stated:

“This was a really challenging extraction, in fact we’d previously felt was too difficult to collect the fossil, but I thought it was really important to study it. I was able to persuade the team to give it a try. It took a lot of hard work from a lot of people, but we did it: finally we can confirm and publish Scotland’s first recorded and most complete dinosaur, and that makes it all worthwhile”.

Cerapodan or Ornithopod Dinosaur

The ornithischian (bird-hipped) clade of the Dinosauria has been subdivided into several groups.  Although the exact taxonomy remains undetermined, most palaeontologists distinguish two main groups. Firstly, there is the Thyreophora which comprises the armoured dinosaurs. In addition, there is the Cerapoda which can be further divided into the Ornithopoda and the Marginocephalia (ceratopsids and pachycephalosaurs).

The partial ilium and a histological analysis of fossil bone led the team to conclude that NMS G.2023.19.1 was definitely ornithischian and probably an early ornithopod. Ornithopods were much more common in the Early and Late Cretaceous.  Famous ornithopods such as Iguanodon, Hypsilophodon and Mantellisaurus are associated with Lower Cretaceous deposits.

A Mantellisaurus scale drawing.  An illustration of an Early Cretaceous ornithopod.  Picture credit: Everything Dinosaur

Picture credit: Everything Dinosaur

The ornithopod illustration (above) is based on the CollectA Age of Dinosaurs Mantellisaurus model that was introduced in 2018.  This was the same year when the fossil was removed from its difficult to access location.

To view the range of CollectA Age of Dinosaur figures, including many ornithopods: CollectA Age of Dinosaurs Figures.

Late Cretaceous ornithopods were extremely successful.  Hadrosaurs became the dominant herbivores in many ecosystems.  The Hadrosauridae family (duck-billed dinosaurs) had a global distribution. Some of these dinosaurs were enormous.  For example, Shantungosaurus from the Late Cretaceous of China reached lengths in excess of fourteen metres.

The Elgol Dinosaur Fossil

The Elgol fossils suggest an animal about the size of a pony.  Histological analysis concluded that the animal was at least eight years of age when it died. The new description of the Elgol dinosaur is published in the Earth and Environmental Science Transactions of the Royal Society of Edinburgh. If the fossil material does represent an ornithischian, as tentatively suggested from the partial ilium and histological sectioning, it represents the geologically youngest known occurrence in Scotland, and first from the Kilmaluag Formation.  This adds to the diversity of dinosaurs known from the Middle Jurassic of the Isle of Skye.

To read an article about the types of dinosaurs that lived in this part of the world during the Middle Jurassic: Tracks of Middle Jurassic Dinosaurs.

A close-up view of the 166-million-year-old Elgol dinosaur fossil. Dr Elsa Panciroli carefully examines the fossil material. Picture credit: Neil Hanna.

Picture credit: Neil Hanna

Co-author of the study, Dr Stig Walsh (National Museums Scotland) said:

“This is a wonderful addition to the rapidly growing set of Jurassic finds from the Isle of Skye which are enabling us to learn more and more about the rich ecosystem of the time. We’ve known there were dinosaurs there for a while, most obviously from the famous footprints at An Corran, Brother’s Point and Duntulm and from individual bones, but it’s exciting to see a more complete, if still partial, skeleton. We’re delighted to add it to the other amazing finds now in the National Collection”.

Other recent Jurassic discoveries from Skye include the description of adult and juvenile mammals of the same species, Krusatodon, which revealed that these mammals grew more slowly than mammals today, and possibly one of the world’s largest Jurassic pterosaurs, Dearc sgiathanach.

To read Everything Dinosaur’s article about the Krusatodon fossils: Providing an Insight into Krusatodon Ontogeny.

To read about the discovery of D. sgiathanach: Fantastic Pterosaur from the Isle of Skye.

More Dinosaur Fossils?

Fellow author Professor Susie Maidment of the London Natural History Museum and the University of Birmingham, added:

“The Elgol dinosaur was a challenge to collect, and has proven perhaps an even bigger challenge to identify. Some aspects of the bones indicate that the specimen may be an ornithopod, a group of plant-eating dinosaurs that are best known from the Cretaceous. This specimen, however, would already have been a fossil by the time that the better-known ornithopods like Iguanodon and Hypsilophodon were walking the Earth. Recent research on the fossils of Elgol has revealed a diverse ecosystem of extraordinarily preserved Middle Jurassic animals, and I’m sure there are more exciting discoveries to come.”

The other authors on the paper were Professor Roger Benson (American Museum of Natural History), Professor Richard Butler (University of Birmingham), Brett Crawford (Research Casting International – RCI), Matt Fear (RCI), Dr Nick Fraser (National Museums Scotland) and Dr Gregory Funston (Royal Ontario Museum).

With the description of the Elgol dinosaur fossil, the significance of the Isle of Skye is once again emphasised.  Furthermore, it demonstrates the importance of this part of Scotland in terms of learning more about the dinosaur biota from the Middle Jurassic.

Everything Dinosaur acknowledges the assistance of a media release downloaded from National Museums Scotland.

The scientific paper: “The first and most complete dinosaur skeleton from the Middle Jurassic of Scotland” by Elsa Panciroli, Gregory F. Funston, Susannah C. R. Maidment, Richard J. Butler, Roger B. J. Benson, Brett L. Crawford, Matt Fair, Nicholas C. Fraser and Stig Walsh published in the Earth and Environmental Science Transactions of The Royal Society of Edinburgh.

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