T. rex Never Stopped Growing, Dinosaur Bone Study Suggests

"Dinosaur bones are like treesevery year is represented by a new ring, and paleontologists can count those concentric circles to determine a fossil's age. But new research suggests that in the case of Tyrannosaurus rex, some growth rings have escaped detection until now. That means the king of the tyrant lizards lived longer than experts realizedand never stopped growing larger."

"Previous estimates put T. rex's lifespan at about 30 years, and the dinosaurs were thought to have reached their full size around age 20 to 25. The new research, published today in PeerJ, rewrites that life cycle: bones from 17 specimens indicate that these hulking predators actually stopped growing sometime between 35 and 40 years old and typically reached at least 8.8 tons."

"The clues lay hidden in T. rex leg bones all along: while some growth rings can be seen with visible light, others, it turns out, only reveal themselves in cross-polarized light. Past research overlooked these fainter rings. Holly Woodward, a paleontologist at Oklahoma State University and lead author of the new study, almost did, too. I sort of discounted it at first, she says, until I started looking at all these specimens and seeing it in a lot of them."

Dinosaur leg bones preserve annual growth rings that can be counted to estimate age, but some rings are only visible under cross-polarized light. Examination of 17 Tyrannosaurus rex leg bones that included these subtler rings shows that growth continued longer than previously estimated. T. rex individuals typically stopped growing between 35 and 40 years and commonly reached masses of at least 8.8 tons. Earlier estimates of a 30-year lifespan and full size by 20–25 years underestimated longevity and size because fainter growth marks were overlooked. Subtler rings may indicate temporary slowdowns rather than complete pauses in growth.

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