King of the dinosaurs
October 17, 2011
New models published last Thursday in the scientific journal PLoS One show that Tyrannosaurus rex grew twice as fast as previously thought.
Based on laser scans comparing juvenile and adult skeletons, an international research team found that the "king tyrant" was bigger than estimated thus far, also possessing different body mechanics.
This could lend further credence to the theory that agile juvenile T. rex hunted in packs, while adults were more likely solitary ambush predators.
Skeletal scans
The research team, led by John Hutchinson at the Royal Veterinary College outside of London, began with three-dimensional laser scans of T. rex skeletons.
"Really, we just used the skeleton as a guide," Hutchinson told Deutsche Welle. Hutchinson said his team "wrapped the flesh around" the extremely accurate scans, based on general biomechanical principles and on the best data from living animals.
The end product is a much more robust T. rex than previous models suggested. While former estimates put a mature adult at 5 to 7 metric tons, the new research says this was probably closer to 9.
Heinrich Mallison, who researches dinosaurs at the Museum für Naturkunde in Berlin and was not involved in the study, upheld the college's conclusions.
"A lot of these classic dinosaur reconstructions are under-muscled," he told Deutsche Welle.
Not only that, but T. rex also grew at an astonishing rate, gaining up to 5 kilograms a day.
Voracious teenagers
To estimate the growth rate, the scientists compared the skeleton of juvenile T. rex "Jane" with that of adult T. rex "Sue," which are housed at different museums in Illinois, in the United States.
The research team also included paleontologists from the University of Liverpool, and from the Field Museum in Chicago.
For Jane to become Sue, they estimated she would have had to put on 1,790 kilograms per year during growth spurts in her "teenage" years, at around 14 years old.
The T. rex reached full maturity at around 17 years of age, and could have survived to be as old as 35.
"I wouldn't be surprised if it had to eat 50 kilograms of meat a day," Hutchinson said of the hungriest periods of a growing T. rex's life.
Duck-billed dinosaurs, triceratops and smaller creatures would have made up the animal's diet, he explained.
How it hunted is still not clear, although the dominant theory is that slim juveniles were suited to pack hunting, and adults to solitary ambushes.
Thunder thighs
As a typical T. rex got older and increased in mass, it's likely to have slowed down, the research indicates. One conclusion of the new paper is also that the animal became more front-heavy as its center of gravity shifted forward.
With relatively small rear limbs compared to its body, the legs had to be quite beefy to support the strong musculature.
This gave T. rex "some of the biggest [leg muscles] of all land mammals, as a percentage of body weight," Hutchinson said – twice as big as a rhinoceros or giraffe, he added.
This made adult T. rexes "optimized for a different hunting role," Mallison asserted.
This "forward shift of the center of gravity could allow for more momentum and power to accelerate quickly and knock over prey," Mallison said, adding to the idea that adults could have been solitary hunters.
"The big ones are ambush predators," Mallison said, explaining that the hunter just has to make those last few meters before its prey reacts.
"The slim-limbed ones are the chasers," he said, adding that comparison of lions and tigers upholds this idea.
Massively muscled tigers take a solo ambush approach, in contrast with the more active pack hunting of longer-limbed lions, for example.
The incredible growth rates also uphold the idea that T. rex was warm-blooded – though not a mammal, Mallison said. A closest comparison could be a bird.
Terrifying tyrant
Hutchinson added that the next step in research is to develop the same types of models for earlier species of tyrannosaurs, to see how they evolved into the terrifyingly massive T. rex.
And the method of laser scanning with 3-D modelling is "the way of the future," Mallison added.
In terms of the fear factor, the Tyrannosaurus rex has got to be in the top five most terrifying predators in history, Hutchinson said.
"Killer whales are pretty scary, lions are pretty scary - but this was one of the biggest land predators ever," Hutchinson concluded.
Author: Sonya Angelica Diehn
Editor: Cyrus Farivar