"A fossil once assumed to be of a young Tyrannosaurus rex is in fact that of a different species altogether, and the dinosaur it belongs to was a fully grown adult at the time of its death, palaeontologists have found. The small tyrannosaur - named Nanotyrannus - is about half the length and one-tenth of the body mass of a fully grown T. rex - which led scientists to initially suspect the fossil belonged to a teenage T. rex."
"But the specimen has several distinct physical features, too. " Nanotyrannus is a small-bodied predator designed for speed. It's very agile and has long powerful arms [that are] larger than those of the T. rex," says Lindsay Zanno, a palaeontologist at North Carolina State University in Raleigh. Nanotyrannus also had a shorter tail than did T. rex and sharper, less curved teeth."
A fossil previously assumed to be a juvenile Tyrannosaurus rex has been identified as Nanotyrannus, a separate small tyrannosaur species. Nanotyrannus measured about half the length and one-tenth the body mass of a full-grown T. rex. The specimen exhibits distinct anatomy including relatively long, powerful arms, a shorter tail, and sharper, less curved teeth indicative of speed and agility. Growth-ring analysis of a thin bone slice showed growth patterns consistent with adulthood, using comparisons to crocodilian growth rates. The fossils originate from the Hell Creek Formation and date to roughly 67 million years ago.
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