Researchers have described a new theropod dinosaur from the Cerro del Pueblo Formation (Coahuila, northern Mexico).  The dinosaur has been named Mexidracon longimanus.  It is the first ornithomimid to be named from fossils associated with the Cerro del Pueblo Formation. The most conspicuous characteristics of this new taxon are the exceptionally long metacarpal bones.  These are the bones that form the palm of the hand.  The hands of Mexidracon longimanus were long and slender.  Furthermore, the hands were longer than the humerus (upper arm bone).  It is not known what these slender hands were used for, although it has been speculated that they helped this toothless dinosaur forage for food.

A scale drawing of the newly described ornithomimid dinosaur from the Cerro del Pueblo Formation (Mexico). Although known from only fragmentary remains it is thought this dinosaur was feathered. It is estimated to have stood around one metre tall and measured two and half metres long. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

Mexidracon longimanus – the first ornithomimid formally described from Coahuila

In 2014, Professor Claudio de León-Dávila collected postcranial ornithomimid remains from a deposit representing an estuary environment.  These fossils are currently housed in the collection of the Benemérita Escuela Normal de Coahuila (BENC), a teacher training institution in Coahuila state. Ornithomimosaur remains are relatively common in the Campanian Cerro del Pueblo Formation, although most of the material is highly fragmentary.

To date only one other ornithomimosaur has been described from the region. Paraxenisaurus normalensis was scientifically described in 2020 (Serrano-Brañas et al).  It is represented by elements from the hands, limbs, including the distal end of a femur, and caudal vertebrae.  P. normalensis is thought to be much larger than the newly described Mexidracon.  Moreover, it has been tentatively assigned to the Deinocheiridae family within the Ornithomimosauria clade. Whereas, Mexidracon longimanus has been assigned to another family, the Ornithomimidae.

A model of Deinocheirus.  The figure is from the CollectA Age of Dinosaurs Popular range.

The image (above) shows the CollectA Age of Dinosaurs Popular Deinocheirus figure.  It is thought that Paraxenisaurus normalensis may have been related to this Asian deinocheirid.

To view the CollectA Age of Dinosaurs Popular range available from Everything Dinosaur: CollectA Prehistoric Animal Models.

The Etymology of a Dinosaur Name

The genus name is derived from the prefix “Mexi”, a reference to Mexico and the suffix “dracon”.  This is from the Greek, and it means serpent or dragon.  The species or trivial name translates as “long hands”.  So, this new theropod’s name translates as “long-handed Mexican dragon.”

The researchers conclude that the discovery of the first ornithomimid in this region of Mexico suggests that during the Campanian faunal stage of the Cretaceous there was a large number of different ornithomimosaurs present.

The scientific paper: “A long-handed new ornithomimid dinosaur from the Campanian (Upper Cretaceous) Cerro del Pueblo Formation, Coahuila, Mexico” by Claudia Inés Serrano-Brañas, Belinda Espinosa-Chávez, Claudio de León-Dávila, S. Augusta Maccracken, Daniela Barrera-Guevara, Esperanza Torres-Rodríguez and Albert Prieto-Márquez published in Cretaceous Research.

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A fossilised cervical vertebra from a pterosaur preserves a bite mark from a crocodilian.  The neck bone was discovered during an international field course in the famous Dinosaur Provincial Park Formation (Alberta, Canada), that took place in July 2023.  The course was led by Dr Brian Pickles from the University of Reading.  The fossil bone preserves a four-millimetre-wide puncture mark from a crocodilian tooth.  The punctured vertebra probably represents a bone from a juvenile Cryodrakon boreas.

The juvenile Cryodrakon boreas neck bone (bottom right) with an adult neck bone (top). Picture credit: University of Reading.

Picture credit: University of Reading

The researchers estimate that this animal had a wingspan of around two metres.  However, much larger pterosaur bones from the Dinosaur Park Formation suggest that a fully-grown Cryodrakon could have rivalled Quetzalcoatlus in size.  Indeed, when azhdarchid pterosaur bones were first discovered in this formation, the material was tentatively assigned to Quetzalcoatlus spp.

To read Everything Dinosaur’s blog post from 2019 about the discovery of Cryodrakon boreas: The First Pterosaur Unique to Canada.

A Juvenile Cryodrakon boreas

The study was undertaken by researchers from the Royal Tyrrell Museum of Palaeontology (Alberta), the University of Reading (UK) and the University of New England (Australia). The paper has been published today.  The circular nature of the bite mark and other aspects of its morphology indicate that it was made by a crocodilian tooth.  It is not known whether this is evidence of predation or whether the crocodilian scavenged a pterosaur carcase.  However, it is remarkable evidence of predator/prey dynamics dating from the Late Cretaceous.

Lead author of the paper, Dr Caleb Brown (Royal Tyrrell Museum of Palaeontology), commented:

“Pterosaur bones are very delicate – so finding fossils where another animal has clearly taken a bite is exceptionally uncommon. This specimen being a juvenile makes it even more rare.”

Research team members working at the quarry where the juvenile Cryodrakon boreas cervical vertebra was found. Picture credit: University of Reading.

Picture credit: University of Reading

Fossils from this strata date from the Campanian faunal stage of the Late Cretaceous.  This young pterosaur lived approximately seventy-six million years ago.

Comparing Pterosaur Bones and Using Micro-CT Scans

The scientists compared the single vertebra with other pterosaur bones to confirm that the puncture did indeed represent pathology.  Evidence of an actual bite into the bone.  Micro-CT scans were employed to permit a much more detailed analysis of the puncture wound.

Co-author Dr Brian Pickles (University of Reading) explained:

“Bite traces help to document species interactions from this period. We can’t say if the pterosaur was alive or dead when it was bitten but the specimen shows that crocodilians occasionally preyed on, or scavenged, juvenile pterosaurs in prehistoric Alberta over 70 million years ago.”

This is the first documented evidence from North America of ancient crocodilians opportunistically feeding on pterosaurs.  Azhdarchid bones with possible crocodilian bites have previously been recorded in Romania.

A researcher carefully brushes away debris from a fossil bone at a quarry located in the Dinosaur Provincial Park Formation. Picture credit: University of Reading.

Picture credit: University of Reading

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

The scientific paper: “A juvenile pterosaur vertebra with putative crocodilian bite from the Campanian of Alberta, Canada” by Caleb M. Brown, Phil R. Bell, Holly Owers and Brian J. Pickles published in the Journal of Palaeontology.

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