India, Jan. 16 -- For decades, scientists have estimated the age and growth rate of Tyrannosaurus rex by counting annual growth rings-similar to those found in trees-preserved inside fossilized leg bones. These rings have long been used to determine how old the giant carnivores were when they died and how rapidly they matured.

"Best estimates from previous studies suggested that T. rex typically stopped growing around age 25," said Dr. Holly Woodward, professor of anatomy and paleontology at the Oklahoma State University Center for Health Sciences and lead author of the new study.

However, an extensive analysis of 17 tyrannosaur specimens-ranging from early juveniles to massive adults-reveals that the iconic predator took nearly 40 year...