Tyrannosaurus rex (illustration from Wikimedia)

4 March 2026

How long did Tyrannosaurus rex typically live? Until recently, research had pegged their life span at 28-30 years but a new study finds that T-rex did not reach full size until age 40, ten years after it should have died. The previous life span is open to debate.

Dinosaur bones have concentric growth rings (cortical growth marks, CGM) like the rings found in tree trunks. To count the bone rings (CGM), the team obtained slices of leg bones from 17 specimens and ground them so thin that light could shine through them. Illustration below: Pink and blue arrowheads point to growth rings below. Notice that the bone slice is shaped like a ring. Dinosaur bones are hollow, just like bird bones!

Earlier bone studies had ignored or not even seen the tightly packed rings so they estimated the life span at 28-30 years. This study counted everything. That’s how they reached 40.

So how large is a full size T-rex? It weighed 8 tons and “shook the earth when it walked.”

Sue, the most complete fossil skeleton of a Tyrannosaurus Rex specimen ever found, Chicago Field Museum (photo from Wikimedia with white background)

What else weighs 8 US tons? This top-of-the-line Bobcat compact (mini) excavator E88.

Bobcat E88 Compact Excavator (photo embedded from Bobcat North America)

They kind of resemble each other, eh?

Read more at allthatsinteresting.com and PeerJ.