A comprehensive analysis of 17 fossil specimens reveals that Tyrannosaurus rex grew far more slowly than previously thought — reaching its full-grown size of eight tons around age 40 — and challenges earlier assumptions about its life history.
Tyrannosaurus rex holotype specimen at the Carnegie Museum of Natural History, Pittsburgh, the United States. Image credit: Scott Robert Anselmo / CC BY-SA 3.0.
Tyrannosaurus rex, one of the most iconic non-avialan dinosaurs, remains a central focus of paleobiological research.
Previous growth modeling studies suggested the ancient predator exceeded eight tons within two decades and had a lifespan approaching 30 years.
The new analysis was able to assemble a more complete and accurate picture of the dinosaur’s growth by using advanced statistical algorithms and examining slices of bone under a special kind of light, which reveals hidden growth rings not counted in previous studies.
In addition to extending the growth phase of Tyrannosaurus rex by 15 years, the results suggest that some of the specimens may not be Tyrannosaurus rex at all, but rather members of other species or different for some other reason.
“This is the largest data set ever assembled for Tyrannosaurus rex,” said Oklahoma State University Professor Holly Woodward.
“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 Tyrannosaurus rex bone records only the last 10 to 20 years of the animal’s life.
“We came up with a new statistical approach that stitches together growth records from different specimens to estimate the growth trajectory of Tyrannosaurus rex across all stages of life in greater detail than any previous study,” said Dr. Nathan Myhrvold, a mathematician and paleobiologist at Intellectual Ventures.
“The composite growth curve provides a much more realistic view of how Tyrannosaurus grew and how much they varied in size.”
Rather than racing to adulthood, Tyrannosaurus grew more slowly and steadily than previously believed.
“A four-decade growth phase may have allowed younger tyrannosaurs to fill a variety of ecological roles within their environments,” said Dr. Jack Horner, a researcher at Chapman University.
“That could be one factor that allowed them to dominate the end of the Cretaceous period as apex carnivores.”
The team’s results were published online this week in the journal PeerJ.
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H.N.Woodward et al. 2026. Prolonged growth and extended subadult development in the Tyrannosaurus rex species complex revealed by expanded histological sampling and statistical modeling. PeerJ 14: e20469; doi: 10.7717/peerj.20469
