New Bird-Like Dinosaur Discovered: Overoraptor chimentoi

Thursday, June 11, 2020

Life reconstruction of an adult and a juvenile Overoraptor chimentoi. Image credit: Gabriel Lio.

A new genus and species of paravian theropod dinosaur has been identified from fossils found in Patagonia, Argentina.

The newly-discovered dinosaur roamed the Earth some 90 million years ago during the Cretaceous period.

Scientifically named Overoraptor chimentoi, the ancient creature was a gracile theropod, approximately 1.3 m (4.3 feet) in length.

It had very long and graceful arms, legs well adapted for running, and Velociraptor-like sickle claw on the second toe.

“This feature is not present in birds, whose legs — more advanced in evolutionary terms — allow them to hold onto tree branches,” said lead author Matias Motta from the CONICET and the Argentine Museum of Natural Sciences ‘Bernardino Rivadavia’ and his colleagues.

Life reconstruction of Overoraptor chimentoi. Image credit: Gabriel Lio.

The fossilized remains of Overoraptor chimentoi were recovered from the beds of the Huincul Formation in the Patagonian province of Rio Negro. The specimens were found in association with crocodilian and turtle bones.

“There are characteristics that distinguish Overoraptor chimentoi from the unenlagiid theropods of Argentina as well as from non-South American raptors such as Velociraptor,” said Dr. Fernando Novas, also from the CONICET and the Argentine Museum of Natural Sciences ‘Bernardino Rivadavia.’

“When analyzing its arms, we found avian features related to the flight. This leads us to consider that in a phylogenetic tree, Overoraptor chimentoi is closer to birds than most of the raptors known so far.”

“Our hypothesis is that in the case of Overoraptor chimentoi, its ability to automatically fold the wings must have had a different function than it does in flying birds, given it is a running animal,” Motta added.

“It is possible that the dinosaur’s arms had the role of guaranteeing balance during the race — by providing greater balance and precision — thanks to the possibility of moving them in a consistent manner, as happens in running birds such as the rhea or ostriches.”

“Certain characteristics of the bones of Overoraptor chimentoi’s arms, particularly the ulna, make them more similar to the wings of birds, such as those of the rheas and condors, than to other raptor dinosaurs, including unenlagiids.”

Silhouette of Overoraptor chimentoi showing selected skeletal elements. Scale bars – 50 cm in the silhouette, 4 cm in (a, b, d, h, and j), and 2 cm in (c, e, f, g, and i). Image credit: Motta et al, doi: 10.1007/s00114-020-01682-1.

The paleontologists also found that Overoraptor chimentoi is closely related to Rahonavis, a paravian theropod dinosaur that lived 70 million years ago (Cretaceous period) in what is now northwestern Madagascar.

“Both species had raptor-type legs and arms similar to the wings of birds, which means an evolutionary advance absent in both unenlagiids and velociraptors,” Dr. Novas said.

“We think that due to its anatomical characteristics, Rahonavis must also have had the ability to perform the automatic folding of the wing, typical of birds,” Motta said.

“These similarities would indicate that Overoraptor chimentoi and Rahonavis could form a new group of paravian runners, which would be closer to the birds than known raptor families.”

The discovery is reported in a paper in the journal Science of Nature.


M.J. Motta et al. 2020. New theropod dinosaur from the Upper Cretaceous of Patagonia sheds light on the paravian radiation in Gondwana. Sci Nat 107, 24; doi: 10.1007/s00114-020-01682-1