We all know Tyrannosaurus rex was a giant—possibly the heaviest land predator ever. But how fast did it reach that monstrous size?
Turns out, the answer is slower than you might think.
A new study examining the leg bones of 17 T. rex fossils suggests these predators took around 40 years to max out at roughly 8 tons.
This is about 15 years longer than earlier estimates.
The researchers, using polarized light to spot previously invisible growth marks, discovered a surprisingly gradual growth pattern.
“This growth trajectory is more gradual than expected,” said Holly Woodward, lead author and paleohistologist at Oklahoma State University.
“Rather than T. rex shooting up to adult size quickly, it spent much of its life in juvenile or subadult stages.”
T. Rex Growth Patterns
The team analyzed annual growth rings, similar to tree rings, and found variability from year to year.
“Some years, a T. rex barely grew. Other years, it grew a lot,” Woodward explained. “It depended on food availability and environmental conditions.
When times were tough, it conserved energy. When resources were plentiful, it bulked up—allowing it to outcompete other predators.
Eventually, only other T. rex stood in its way.
So next time you picture a rampaging T. rex, remember: it didn’t always go full monster mode.
Even the fiercest predator had a slow-growth phase, proving that sometimes, patience really is a survival strategy.
