Newly examined ‘teenage’ Tyrannosaurus rex bones reveal how dinosaur became the ultimate monster

According to researchers, the juvenile tyrannosaurs would have been ‘slightly taller than a draft horse and twice as long’

Nilima Marshall
Wednesday 01 January 2020 20:02
Illustration of the juvenile T rex dinosaurs, quite unlike their lumbering adult counterparts
Illustration of the juvenile T rex dinosaurs, quite unlike their lumbering adult counterparts

Bones belonging to two “teenage” Tyrannosaurus rex dinosaurs provide fresh clues as to how these predators grew up to become “plodding, crushing monsters”, according to a new study.

The fossil skeletons indicate the juvenile T rex dinosaurs were slender, fleet-footed and had knife-like teeth for cutting food, unlike their lumbering, bone-crushing adult counterparts.

It was previously believed that the bones, which are preserved at the Burpee Museum of Natural History in Illinois, US, belonged to a different dinosaur species, a smaller pygmy relative known as Nanotyrannus.

But an examination of the tissue microstructures within the bones revealed they were part of the T rex family.

Dr Holly Woodward, an associate professor of anatomy at the Oklahoma State University Centre for Health Sciences and lead author on the study, said: “Historically, many museums would collect the biggest, most impressive fossils of a dinosaur species for display and ignore the others.

“The problem is that those smaller fossils may be from younger animals.

“So, for a long while we’ve had large gaps in our understanding of how dinosaurs grew up, and T-rex is no exception.”

According to the researchers, the juvenile tyrannosaurs would have been “slightly taller than a draft horse and twice as long” and were yet to experience a major growth spurt at the time of their death.

A thin slice of bone (inset) which has been removed from the tibia of the T rex ‘Jane’, and examined with a microscope

Adult T rex, on the other hand, would have been around 40ft long and 15ft to 20ft tall, making them one of the largest meat-eating dinosaurs that ever lived.

Scott Williams, a palaeontology lab and field specialist at Museum of the Rockies in Montana, US, and study co-author, said their findings show these dinosaurs “go through a drastic change when they grow up from these sleek, slender, fleet-footed T rexes with these wonderful knife-like teeth to these big, monster, plodding, crushing tyrannosaurs that we are familiar with.

“It also tells us these animals probably dominated their ecosystems at all ages.”

To assess the age and growth rate of the T rex specimens, nicknamed “Jane” and “Petey”, the researchers removed thin slices from the leg bones and examined them at high magnification.

They found that by counting the annual rings within the bone, much like counting tree rings, Jane and Petey were teenagers when they died, aged 13 and 15, respectively.

Newly discovered species of dinosaur has bat-like wings

Based on their analysis of the bones, the researchers believe it took the T rex up to 20 years to reach adult size, undergoing drastic changes as it matured.

And based on the spacing in the rings, the team believe the T rex’s growth was dependent on its food source.

For instance, if food was plentiful, the dinosaurs would bulk up, and if food was scarce it would not grow as much.

Dr Woodward said: “The spacing between annual growth rings record how much an individual grows from one year to the next.

“The spacing between the rings within Jane, Petey, and even older individuals is inconsistent – some years the spacing is close together, and other years it’s spread apart.”

The findings are published in the journal Science Advances.

Press Association

Register for free to continue reading

Registration is a free and easy way to support our truly independent journalism

By registering, you will also enjoy limited access to Premium articles, exclusive newsletters, commenting, and virtual events with our leading journalists

Already have an account? sign in

By clicking ‘Register’ you confirm that your data has been entered correctly and you have read and agree to our Terms of use, Cookie policy and Privacy notice.

This site is protected by reCAPTCHA and the Google Privacy policy and Terms of service apply.

Join our new commenting forum

Join thought-provoking conversations, follow other Independent readers and see their replies


Thank you for registering

Please refresh the page or navigate to another page on the site to be automatically logged inPlease refresh your browser to be logged in