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.

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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.

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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.