A new species of Patagonian megaraptor has been described.  Joaquinraptor casali provides further insight into this enigmatic Cretaceous dinosaur family.  The fossil material casts light on these giant-clawed theropods, as this is only the second member of the Megaraptoridae family to have been discovered with extensive skull remains.  The study has been published in the journal “Nature Communications”.

Intriguingly, the field team found a crocodyliform humerus between the lower jaw bones of Joaquinraptor.  This suggests that that the new megaraptor may have been eating the crocodyliform when it died.  However, this is only an assertion, it is not definitive.  The limb bone could have ended up lodged between the dentaries as a result of being washed into the submerged mouth of the dinosaur’s carcase.

Joaquinraptor casali life reconstruction. The new megaraptor dinosaur species Joaquinraptor casali in what is now central Patagonia, Argentina roughly 67 million years ago. The carnivore holds a crocodyliform (= extinct crocodile relative) front leg in its mouth, in keeping with the discovery of a crocodyliform forelimb bone between the lower jaws. Picture credit: Andrew McAfee, Carnegie Museum of Natural History.

Picture credit: Andrew McAfee, Carnegie Museum of Natural History.

The upper arm bone of the crocodyliform bears tooth marks and the bone was touching some of the megaraptor’s teeth.  So, some kind of interspecific interaction seems likely. Perhaps, the theropod and the crocodyliform were fighting.  For example, the two predators could have been battling over a food resource.

Possible evidence of diet or predation in the new megaraptor dinosaur species Joaquinraptor casali. (a) Dentaries (= tooth-bearing lower jaw bones) of Joaquinraptor and an associated crocodyliform (= extinct crocodile relative) forelimb bone in the position in which they were found, prior to their separation in the laboratory. Detail (b) view showing a portion of the croc forelimb bone in contact with the teeth of Joaquinraptor. The croc bone (c) after its separation from the Joaquinraptor dentaries. Picture credit: Lucio M. Ibiricu et al.

Picture credit: Lucio M. Ibiricu et al

Joaquinraptor casali

Joaquinraptor seems to be quite typical for a megaraptor.  It had a long, low skull lined with serrated teeth and powerful forelimbs. The two innermost talons of the hand were tipped with large claws.  The genus name honours Joaquín, the son of the first author (Lucio M. Ibiricu) and the informal name given to the locality when the skeleton of the taxon was discovered (Valle Joaquín). Dr Gabriel Andrés Casal inspired the species epithet.  Dr Casal has made a significant contribution to our understanding of Cretaceous dinosaurs from Argentina.  In addition, he was responsible for the formal recognition and naming of the formation from which this megaraptorid was recovered (the Lago Colhué Huapi Formation).

A skeletal reconstruction of the new megaraptor dinosaur species Joaquinraptor casali showing the bones preserved (in blue). Other parts of the skeleton and body outline silhouette are based on closely related species. Photos of many of the preserved bones in various views surround the skeletal reconstruction. Skeletal reconstruction by T.K. Robinson and Andrew McAfee. Picture credit: Lucio M. Ibiricu et al.

Picture credit: Lucio M. Ibiricu et al

The Geologically Youngest Member of the Megaraptoridae

The researchers estimate that Joaquinraptor was around seven metres in length.  It probably weighed a tonne. This newly described theropod is also likely to be the geologically youngest megaraptor ever discovered.  Megaraptors survived until the end of the Cretaceous, 66 million years ago.  The partial, skeleton comes from the Chubut Province (southern Patagonia).  It was studied by Dr Lucio Ibiricu of Argentina’s Instituto Patagónico de Geología y Paleontología, and several other scientists including Dr Matt Lamanna of the Carnegie Museum of Natural History.

Dr Lamanna commented:

“At the Carnegie Museum of Natural History, we’re always seeking to better comprehend the history of life on our planet.  Every year, our team of experts conducts field work all over the world, helping to ensure that we’re on the cutting edge of research.  New revelatory dinosaur discoveries, like Joaquinraptor casali, deepen our understanding of how extraordinary creatures lived and advance understanding of the natural world, both past and present.”

Fossils of the new megaraptor dinosaur species J. casali in the quarry, laying in the positions they had laid for approximately 67 million years. A dentary, teeth, ribs, and several other bones are visible. Picture credit: Marcelo Luna, Laboratorio de Paleontología de Vertebrados Dr. Rubén Martínez, Universidad Nacional de la Patagonia San Juan Bosco.

Picture credit: Everything Dinosaur

An analysis of a cross section of the tibia revealed that this dinosaur was at least nineteen years old when it perished. However, whilst the researchers considered the specimen to have been sexually mature, it was not fully grown.

Everything Dinosaur acknowledges the assistance of a media release from the Carnegie Museum of Natural History in the compilation of this article.

The scientific paper: “Latest Cretaceous megaraptorid theropod dinosaur sheds light on megaraptoran evolution and palaeobiology” by Lucio M. Ibiricu, Matthew C. Lamanna, Bruno N. Alvarez, Ignacio A. Cerda, Julieta L. Caglianone, Noelia V. Cardozo, Marcelo Luna and Rubén D. Martínez published in Nature Communications.

The Everything Dinosaur website: Dinosaur Models.