Even with a dinosaur as famous as the legendary 40-foot-long T.rex, there can be new discoveries. Until now, scientists believed that a “pygmy” tyrannosaur dubbed Nanotyrannus lived alongside the giant “tyrant king” sixty-six million years ago. Now, after further study, they have concluded that the smaller fossils are actually young T.rex.
The study has revealed new insights into how the monster of the Cretaceous grew, going from the size of a pigeon to the size of a city bus. As they grew, the ravenous teenagers went through irregular growth spurts, dependent on how much food they could capture.
Holly Woodward, Ph.D., from Oklahoma State University Center for Health Sciences, studied the bones of two small T. rex collected from Carter County, Montana in the early 2000s.
The fossils named Jane and Petey and are now thought to be teenage T. rex that died at 13 and 15 years old, respectively, according to the Oklahoma State website. The teenagers were taller than a horse at six feet tall at the time of their premature deaths.
“To me, it’s always amazing to find that if you have something like a huge fossilized dinosaur bone, it’s fossilized on the microscopic level as well,” Woodward said. “And by comparing these fossilized microstructures to similar features found in modern bone, we know they provide clues to metabolism, growth rate, and age.”
— Holly Woodward (@histo_holly) January 3, 2020
The New York Times suggests that the young T.rex had an advantage over their huge, more cumbersome parents. While adults traveled at a fast walk of 10 to 25 mph, the young un’s could breeze by them. However, this meant they probably didn’t compete with their parents since they tackled different types of prey.
The young T. rex also had an evolutionary advantage by limiting periods of growth to the times when there was ample food available.
From the Times:
“A full-grown T. rex was probably the most fearsome sight of the Cretaceous: It stood two stories tall, stretched the length of a city bus and boasted jaws that could crush the bones of a triceratops.
But as with the teenagers of many species, adolescent T. rexes inspired their own form of terror. Fast and light, they could catch prey their parents couldn’t.”
A T. Rex is already nightmare inducing, but OSU-CHS Associate Professor of Anatomy Holly Woodward Ballard's research reveals these predatory dinosaurs also hit the evolution jackpot. When food was scarce, they could slow their own growth. https://t.co/dzuK8aKqCT
— OSU Medicine (@OSUMedicine) January 2, 2020
Since the teenagers could be a variety of sizes, they were able to “dominate their ecosystem at all ages,” according to co-author Scott Williams. By the time it reached adulthood, the tyrant king could chomp straight through solid bone, and could also digest it.
“T. rex babies might eat young herbivores and other small creatures. Teenagers like Jane and Petey caught mid-sized prey. And adults chomped away on herbivore adults.”
Unfortunately for the herbivores of the times, this means T. rex would have been able to tackle prey of just about any size.
From OSU News:
“Juveniles such as Jane and Petey were fast, fleet-footed, and had knife-like teeth for cutting, whereas adults were lumbering bone crushers. Not only that, but Woodward’s team discovered that growing T. rex could do a neat trick: if its food source was scarce during a particular year, it just didn’t grow as much. And if food was plentiful, it grew a lot.”
Although T. rex grew an enormous size during its lifetime, the researchers found that the growth rate was similar to that of modern-day mammals and birds. Business Insider reported that the peak growth spurt probably took place between ages 14 and 18, with a weight gain of 4.6 pounds every day.
“A juvenile T. rex would have weighed about five times more than a 4-year-old boy and was as large as any other predatory dinosaur in its habitat.”
— Holly Woodward (@histo_holly) January 1, 2020
We also know that the young vulnerable T. rex looked very bird-like with a covering of fuzzy feathers.
Illustrations of the baby T. rex look nothing like depictions of the mighty adult T.rex seen in the movies, and those depictions are also not accurate. Adult T.rex might have sported a crest of feathers on its head as well as down the neck and tail.
If anything, the realistic adults seen below from the Museum of Natural History are even more terrifying in appearance. Now we know that the T. rexes were able to terrify almost everything that moved in the Cretaceous, regardless of size or speed.
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