Gualicho shinyae, a newly discovered dinosaur, had extremely tiny arms.
It was a carnivore that stood about six feet tall and weighed about 1,000 pounds, but had arms the size of a human child's, in fact. And while these features were similar to those of T-rex, they evolved independently.
The dinosaur was discovered in northern Patagonia, Argentina, in 2007 and is described in detail by a new report
published Wednesday in the journal PLOS ONE.
"Gualicho is kind of a mosaic dinosaur, it has features that you normally see in different kinds of theropods," Peter Makovicky, The Field Museum's curator of dinosaurs,
said in a news release. "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."
Gualicho is the only known member of the allosaurs group to have small, two-fingered arms.
"It begins to tell us a little bit about the story of how and why animals like T-rex and other theropods reduce their forearms," Makovicky said,
according to The New York Times.
Ancestors of tyrannosaurs had long arms with three digits.
"We don’t actually know what would have triggered a reduction in the forelimb in each individual lineage," he said. "But obviously there was some adaptive advantage because we see it multiple times in different lineages of theropods."
Living in a forested flood plain environment during the Cretaceous Period, the Gualicho probably preyed upon smaller animals than the massive plant-eater Argentinosaurus that also lived during that time,
Reuters reported.