Scientists have concluded that fossils that were once thought to be the skulls of juvenile Tyrannosaurus rexus actually belonged to a different species of dinosaur.
First discovered in Montana ᲩᲕᲜᲜIn 1942, the remains became the subject of debate over whether they were younger than T. Rexes or Nanotyrannus lancensis, smaller relatives of the iconic dinosaurs.
According to research by the University of Bath's Milner Center for Evolution, the fossils were adults dinosaursWhich means the 66 million year old remains are more likely to be from Nanotyrannus.
The university's Dr Nick Longrich said he was “quite surprised” by the findings, based on analysis of growth rings in the fossilized bones and modeling of animal growth.
“I didn't expect it to be so compelling,” he said. “If they were young T-Rex, they should be growing like crazy, gaining hundreds of kilograms a year, but we don't see that.
“We tried to model the data in different ways and continued to see low growth rates.
“This seems to put an end to the hypothesis that these animals are young T. rex.”
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Modeling at the University of Bath, the researchers noted that the dinosaurs studied would have grown to a maximum of 900 to 1,500 kilograms and five meters, about 15% the size of an adult T. Rex.
Dr Longrich added: ‘Just as kittens resemble cats and puppies resemble dogs, different tyrannosaur adults stand out.
“And Nanotyrannus just looks nothing like a T. Rex… The arms are actually longer than T. Rex arms.
Even the largest T-Rex has shorter arms and smaller claws than this tiny Nanotyrannus.
“It was an animal where the gun was a pretty powerful weapon. It's really a completely different animal – small, fast, agile.
“The T. Rex relied on size and strength, but this animal relied on speed.”
The report was published in the journal Fossil Studies.