Researchers are still uncertain why the Tyrannosaurus rex, one of the largest known land predators ever to roam the Earth with the strongest bite force of any terrestrial species, had such tiny forelimbs, but a new study has found that it was not alone in this category.
Writing in the journal PLOS One, Peter Makovicky, dinosaur curator at The Field Museum in Chicago, and his colleagues revealed that they had discovered a new species of dinosaur from Patagonia that, while not a close relative of the T. rex, had similar short, two-fingered claws.
Like tyrannosaurs, the newly-discovered Gualicho shinyae is a theropod, or a two-legged, bird-like type of dinosaurs. However, it belonged to a different branch of the family tree – a group of medium-to-large carnivorous theropods known as allosaurids – which suggests that it developed its short-arms independently rather than through a shared ancestor with the T. rex.
“Gualicho is kind of a mosaic dinosaur, it has features that you normally see in different kinds of theropods,” Makovicky, the study’s corresponding author, said in a statement. He added that the newfound species was “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.”
Experts still unsure why trait is so common among theropods
Discovered in the Huincul Formation of northern Patagonia in 2007 and only now identified as a new theropod species, Gualicho was named in honor of Gualichu, a spirit revered by Patagonia’s Tehuelche people, and Akiko Shinya, chief fossil preparator at The Field Museum’s and the man who originally found the fossilized remains of the creature, the researchers said.
While its skeleton is incomplete, Shinya, Makovicky and their colleagues have determined that it was most likely a medium-sized, approximately 1,000-pound predator that was roughly the same size as a polar bear. It appears to be closely related to Deltadromeus, a carnivorous dinosaur with long legs and slender arms that was found in Africa.
Despite its polar bear-like size, Gualicho‘s forelimbs were said to be similar in size to those of a human child’s, and like the tyrannosaur, it had only a pair of digits (a thumb and forefinger), the researchers noted. Its discovered provides additional evidence that smaller forelimbs had evolved independently on multiple occasions, though scientists still do not know what so many species of theropods seemed to have developed this particular trait.
“By learning more about how reduced forelimbs evolved, we may be able to figure out why they evolved,” said Makovicky, who worked on the research along with colleagues at the 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.
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Image credit: Jorge Gonzalez/Pablo Lara
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