Animals

New Dinosaur Had Tiny T.rex Arms

The 1000-pound dinosaur's arms were the size of a small child's.

<p>Image: Recreation of the new dinosaur <em>Gualicho shinyae</em> eying a smaller duckbilled dino. Credit: Jorge González and Pablo Lara<span></span></p>

Tiny forelimbs were apparently all the rage in the Late Cretaceous, as paleontologists have discovered a new dinosaur that had small Tyrannosaurus rex-like arms.

The new dino, named Gualicho shinyae, shared T. rex's meat-loving ways, according to the paper, published in the journal PLOS ONE. In future, research on it could solve mysteries about its tiny arms as well as those of T. rex and other dinosaurs sporting this look.

"By learning more about how reduced forelimbs evolved, we may be able to figure out why they evolved," co-author Peter Makovicky, who is The Field Museum's curator of dinosaurs, said in a press release.

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Image: The new dinosaur Gualicho showing the fossils that were found along with its other likely anatomy. Credit: Jorge González and Pablo Lara

The research team consisted of an international group of researchers from The Field Museum, Universidad Maimónides in Argentina, the Dinosaur Institute at the Natural History Museum of Los Angeles County, and the Gobierno de la Provincia de Río Negro in Argentina.

Akiko Shinya, The Field Museum's chief fossil preparator, found the remains for the dinosaur during an expedition to the fossil-rich Huincul Formation of northern Patagonia. The species name shinyae honors Shinya, while the generic name Gualicho derives from Gualichu, a spirit revered by Patagonia's Tehuelche people.

Photo: Akiko Shinya, the Field Museum's chief fossil preparator for whom the new dinosaur is named, with Gualicho shinyae at the dig site. Credit: Peter Makovicky, The Field Museum

The team joked about "the curse of Gualicho," since they had some bad luck. At one point, a truck even rolled over with scientists inside, but everyone was OK, save for some cuts and bruises.

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The dino Gualicho lived about 100–66 million years ago and was an allosaurid, referring to a type of medium-to-large carnivorous two-legged dinosaurs. The researchers estimate that Gualicho weighed around 1,000 pounds, comparable to the heft of a modern polar bear.

Photo: Researchers at the expedition site, the Huincul Formation of northern Patagonia. Credit: The Field Museum

Despite its large size, Gualicho's forelimbs were the size of a human child's. Like T. rex, it had just two digits: a thumb and forefinger.

Gualicho somewhat resembles the dinosaur Deltadromeus, which was a leggy meat-eater with slender arms from Africa. Makovicky and his colleagues therefore think that it was closely related to Deltadromeus.

"Gualicho is kind of a mosaic dinosaur; it has features that you normally see in different kinds of theropods (two-legged, bird-like dinosaurs)," Makovicky said. "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."

Shinya had this to say about her namesake dino: "We found Gualicho at the very end of the expedition. Pete joked, 'It's the last day, you'd better find something good!' And then I almost immediately was like, 'Pete, I found something.' I could tell right away that it was good."

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