Among the most exciting of recently recognised dinosaurs are the megaraptorans, a mostly Southern Hemisphere group of predatory dinosaurs, or theropods, famed for their massive hand claws.
And this week sees the publication of a new megaraptoran from the Late Cretaceous of Chubut, southern Argentina, named Joaquinraptor casali
Joaquinraptor is one of the best preserved megaraptorans discovered so far. Its remains include much of the skull, forelimb and shoulder region, part of the hindlimbs and some of the spine. It was 7 m long in life and was a young adult at the time of death, the growth rings in its bones suggesting an age of around 20 years. Its limb bones are robust compared to those of other megaraptorans. Its hand claws are strongly curved, as is typical for megaraptorans, with the biggest being 21 cm long along its curved upper edge.
The latest Cretaceous age of Joaquinraptor is significant. It shows that megaraptorans persisted right to the end of the Age of Dinosaurs 66 million years ago. Most megaraptorans are between 100 and 70 million years old, and other Late Cretaceous megaraptoran species are millions of years older than Joaquinraptor.
A major question about megaraptorans is how they captured prey and what they were eating. Their formidably clawed, large forelimbs suggest they were grabbing mid-sized animals or maybe inflicting fatal wounds on large ones. Their small teeth and slender, shallow skulls suggest that they weren’t killing large prey with their jaws. In fact, their skull feature imply reliance on small prey, but this seems at odds with the massive hand claws.
Joaquinraptor might shed light on this issue, since an arm bone from a crocodile-like reptile is preserved within its jaws, the tips of Joaquinraptor’s teeth being literally embedded in the bone.
Ibiricu and colleagues also draw attention to the presence of megaraptorans in diverse environments. Joaquinraptor comes from a humid floodplain that was close to a sea, while other megaraptorans are from arid, inland environments. Maybe this was an especially adaptable group, able to exploit wholly different sorts of prey. They appear to have been especially diverse and abundant in southern South America at a time when other theropod groups were more abundant in habitats further north on the continent.
There is clearly much more to discover about this incredible group. Indeed, discoveries providing additional key information are due to appear soon.
It was named Joaquinraptor casali by Lucio Ibiricu of the Universidad Nacional de la Patagonia in Chubut, its name honours Joaquín Ibiricu, son of the study’s lead author, as well as Valle Joaquín, the discovery site. The species name celebrates the work of Dr Gabriel Andrés Casal, an expert on Patagonian geology and palaeontology.
Main image credit: Andrew McAfee / Carnegie Museum of Natural History