Gualicho shinyae: New Theropod Dinosaur Unearthed in Argentina

A team of paleontologists has found fossil fragments from a remarkable new species of theropod dinosaur that walked our planet around 94 million years ago.

The newly-discovered dinosaur lived during the Upper Cretaceous epoch in what is now northern Patagonia, Argentina.

The creature, which has been named Gualicho shinyae, was a medium-sized predator and weighed around 450 kg (1,000 pounds), comparable to a polar bear.

Fossil remains of the dinosaur were found in rocks from the Huincul Formation, which has yielded many specimens of sauropod and theropod dinosaurs.

Top: reconstruction of skeletal remains of Gualicho shinyae. Left: forelimb elements of Gualicho shinyae– left humerus in (A) anterior, (B) posterior, (C) proximal, and (D) distal views; left ulna and attached semilunate distal carpal in (E) lateral, (F) posterior, and (G) anterior views; left radius in (H) lateral, and (I) medial views. Abbreviations: dpc – deltopectoral crest; ics – intercondylar sulcus; it – internal tuberosity; msh – scar for insertion of m. scapulohumeralis; olp – olecranon process base; sdc – semilunate distal carpal. Right: left manual digits of Gualicho shinyae – digit I phalanges in (A, D) medial, (B, E) lateral, and (C, F) dorsal views; digit II phalanges in (G-I) medial, (J-L) lateral, and (M-O) dorsal views. Abbreviations: clp – collateral ligament pit; ft – flexor tubercle; t – tuber. Image credit: Jorge Gonzalez / S. Apesteguia et al / Sci-News.com.

Gualicho shinyae belongs to a group of medium-to-large bipedal theropod dinosaurs known as allosaurids (Allosauridae).

The dinosaur is very different from the other dinosaurs that lived near it. It looks most like Deltadromeus, a meat-eating theropod dinosaur with slender arms found in northern Africa.

Despite its large size, Gualicho shinyae’s forelimbs were the size of a human child’s, and like the famous theropod dinosaur Tyrannosaurus rex, it had just two digits — thumb and forefinger.

“Gualicho shinyae is kind of a ‘mosaic dinosaur,’ it has features that you normally see in different kinds of theropods,” said team member Dr. Peter Makovicky, of the Field Museum.

“It’s really unusual — it’s different from the other carnivorous dinosaurs found in the same rock formation, and it doesn’t fit neatly into any category.”

While Gualicho shinyae doesn’t explain why so many theropod dinosaurs had reduced forelimbs, it adds to evidence that the trait evolved independently numerous times.

“By learning more about how reduced forelimbs evolved, we may be able to figure out why they evolved,” Dr. Makovicky said.

Dr. Makovicky and co-authors have documented their discovery in a paper published in the journal PLoS ONE.