Might This Unusual Theropod Be The T. Rex's Cousin?
It looks like the T-Rex was not the only theropod from the Mesozoic era to sport short flimsy arms.
According to Scientific American, the Tyrannosaurus rex was among many carnivorous dinosaurs to have short arms. Lindsay Zanno, head of the Paleontology Research Lab at the North Carolina Museum of Natural Sciences, said that short arms are a commonality among theropods.
"There are a lot of different groups of theropods that tend to reduce the size of their hands and their arms or change the way that they're used," said Zanno. With that being said, welcome Gualicho shinyae.
Discovered in Argentina in 2007, Gualicho was noted for having shorts arms - about two feet long. Their arms are "less than the length of the thigh bone, and they have weak muscle attachments and poorly developed articulations indicating they had little strength," described Peter Makovicky, associate curator of dinosaurs at the Field Museum of Natural History in Chicago.
The fingers on Gualicho are similar to the Tyrannosaurus'. The thumb of the dinosaur sports a large claw, while the second finger is smaller.
"It's really cool that the arms of this particular dinosaur are reduced down to basically two fingers like we see in another very famous well-adapted predator that we know of as Tyrannosaurus rex," says Dr. Zanno, who was not part of the research team.
Due to Gualicho's striking similarities to the T. Rex, some researchers wonder if the two are cousins.
"This animal has a kind of mosaic of features. There are aspects of its skeleton that show some affinities with some groups of dinosaurs and some affinities with other groups of dinosaurs, although none of those are really tyrannosaurs," said study co-author Nathan Smith, associate curator at the Dinosaur Institute at the Natural History Museum of Los Angeles County.
According to Stephen Brusatte, a paleontologist at the University of Edinburgh who was not part of the study, there's no reason to believe they are cousins. "It's like if two teenagers from the same town start greasing up their hair to impress girls. It just means they are behaving similarly for similar reasons, not that they are brothers," he said.
Why does Gualicho have such shorts arms though?
"Most theropods with reduced forelimbs, like tyrannosaurs, ceratosaurs, and Carcharodontosaurus are clearly macropredators that rely on their massive skulls for hunting, so it seems likely that the same was true of Gualicho," said Makovicky.
The new study was published in the journal PLOS ONE on July 13.