The largest study ever conducted on the growth of Tyrannosaurus rex reveals that the dinosaur took a far longer and slower route to adulthood than scientists had previously believed.
Researchers have estimated the age and growth rate of Tyrannosaurus rex by examining annual growth rings inside fossilized leg bones, much like the rings seen in trees. Based on earlier analyses, scientists concluded that T. rex usually reached its full size and stopped growing at about 25 years of age.
Rethinking how T. rex grew up
New research now paints a very different picture of how this famous predator matured. A large study examining 17 tyrannosaur fossils, from young juveniles to enormous adults, suggests that T. rex took closer to 40 years to reach its adult mass of roughly eight tons. This work represents the most detailed reconstruction of the dinosaur’s life history to date and was published in the journal PeerJ.
To achieve this, the research team combined advanced statistical modeling with microscopic analysis of bone slices viewed under specialized lighting. This approach revealed previously overlooked growth rings that earlier studies had missed. By extending the known growth period by about 15 years, the findings also raise the possibility that some fossils traditionally classified as T. rex may actually belong to other species, or differ for other biological reasons.
“This is the largest data set ever assembled for Tyrannosaurus rex,” says Holly Woodward, a professor of anatomy at Oklahoma State University who led the research effort. “Examining the growth rings preserved in the fossilized bones allowed us to reconstruct the animals’ year-by-year growth histories.” Unlike the rings visible on a tree stump, a cross-section of T. rex bone records only the last 10 to 20 years of the animal’s life.
