A groundbreaking study of Tyrannosaurus rex fossils has rewritten what humans know about these prehistoric predators and how long they lived millions of years ago.
A study by three US researchers revealed that T. rex didn’t reach their full adult size until around age 40, maturing gradually and steadily over decades rather than stopping abruptly earlier in life.
This means the oldest T. rex likely lived well beyond their 40s, enjoying a prolonged ‘adolescence’ where they kept getting bigger and stronger into middle age.
Before this study, experts believed T. rex stopped growing by age 25, based on earlier counts of bone growth rings that suggested a quicker path to maturity.
However, researchers sliced open fossilized leg bones from these dinosaurs and examined them under special lights to count hidden growth rings, similar to ones people find in trees, that recorded yearly slowdowns in growth.
Using advanced computer models to combine data from multiple T. rex fossils, the team created a more accurate growth curve that accounted for the variations and extra marks caused by extreme factors such as food shortages or environmental stresses.
Nathan Myhrvold, a mathematician from the Oklahoma State University Center for Health Sciences said: ‘Interpreting multiple closely spaced growth marks is tricky.’
‘We found strong evidence that the protocols typically used in growth studies may need to be revised.’
Scientists now believe the Tyrannosaurus rex (Pictured) lived well into their 40s (Stock Image)
By examining the rings found in fossilized bones, scientists were able to count how old 17 dinosaurs were
The bones came from 17 tyrannosaur specimens collected mostly from museums in Montana and North Dakota, including well-known dinosaurs nicknamed ‘Jane’ and ‘Petey’ that showed unusual growth patterns.
The study, published in journal PeerJ, found that the growth rings inside the T. rex bones each showed a year of life, with solid lines marking times when growth completely stopped and fuzzy bands showing when it just slowed down.
To do this, the scientists polished the fossil slices until they were almost see-through, and examined them under a special kind of microscope that uses polarized light, making hidden details in fossils stand out more.
Normally, dinosaur bone growth rings are very hard or impossible to see clearly with regular microscope light, but the special filters created bright colors and sharp contrasts that reveal every ring in stunning detail.
By counting every single mark in the fossils, including extremely close together lines believed to be caused by stress, the team built four different counting methods and used computer models to test which one gave the most consistent picture of the dinosaur lifespan.
The most reliable method showed that T. rex grew much slower than earlier studies claimed, taking about 35 to 40 years to reach their maximum size instead of maturing in their 20s.
During their fastest growth spurt between the ages of 14 and 29, the scientists believe these predators could gain between 800 and 1,200 pounds per year.
However, the overall T. rex growth process now appears to have stretched out over decades.
Slices of the T. rex leg bones were viewed under polarized light to find previously unseen growth rings
After this rapid teenage growth spike, the study concluded that T. rex entered a long ‘subadult’ stage where they kept slowly adding weight and size for another 10 to 15 years before finally becoming full adult dinosaurs.
Study co-author Jack Horner of Chapman University in California added in a statement: ‘A four-decade growth phase may have allowed younger tyrannosaurs to fill a variety of ecological roles within their environments.’
Horner suggested that this slow path to maturity likely let younger T. rex hunt smaller prey, which may have helped them become the top predators at the end of the dinosaur age known as the Cretaceous Period.
However, the team noted that the fossils examined in this study included fossils from the broader ‘Tyrannosaurus rex species complex,’ which may have included more than one species or subspecies that skewed the new growth timeline.
Moreover, the smaller fossils of Jane and Petey showed growth patterns that didn’t match the rest of the fossil group, suggesting they may have actually belonged to a different species, such as the proposed ‘Nanotyrannus.’
