Tyrannosaurus rex reached its colossal size — of up to 42 feet long — by piling on more than three stone a week during a teenage growth spurt, a study found.
Researchers led from the US cut into the fossilised remains of various dinosaurs to measure the growth lines in their bones and track how fast they grew.
Specimens studied included Sue — the largest known T. rex, from the collections of Chicago’s Field Museum — and allosauroids specimens, which grew steadily instead.
Tyrannosaurus Rex reached its colossal size — of up to 42 feet long — by piling on more than three stone a week during a teenage growth spurt, a study found. Pictured, an artist’s impression of an adult and juvenile T. rex more than 66 million years ago
‘We wanted to look at a wide swath of different theropods — two-legged, carnivorous dinosaurs — in order to understand broader patterns of growth and evolution in the group,’ said paper author Tom Cullen.
‘We particularly wanted to understand how some of them got so big — is the way T. rex grew the only way to do it?,’ the former Field Museum palaeontologist asked.
Mammals — including humans — go through a period of extreme growth during youth and then stay the same size after reaching adulthood. In other animals groups, however, this is not always the case.
‘Growth rate really varies, there’s no one size fits all,’ explained Dr Cullen, who is now based at the North Carolina Museum of Natural Sciences.
T. rex and its fellow theropods are related to both modern reptiles and birds — with the latter in essence being ‘living dinosaurs’.
‘Birds have super growth spurts and reach adult size really fast, while reptiles like alligators and various lizards and snakes have extended growth. With them, a really, really big individual is probably really old,’ Dr Cullen added.
Getting big quickly can be a competitive advantage — it makes it easier for the animal to hunt and, at the same time, harder for it to be hunted.
However, putting on a growth spurt also takes a lot of energy and resources — meaning that it is easier to just grow a little, every year, across your whole life.
‘The amount of calories T. rex would have needed during its growth spurt would have been ridiculous,’ said Dr Cullen.
‘Inside the bones as an animal grows there are markings like tree rings that record roughly how old the animal is, how much it’s growing each year and a number of other factors,’ he explained.
In their study, Dr Cullen and colleagues sliced into the fossilised remains of dozens of dinosaurs — from those the the size of dogs and ostriches all the way up to ‘Sue’, the largest and most complete T. rex skeleton ever found.
The fossils came from all over the world — including the US, China and Argentina.
Researchers led from the US cut into the fossilised remains of various dinosaurs to measure the growth lines in their bones and track how fast they grew. Specimens studied included Sue — the largest known T. rex (pictured), from the collections of Chicago’s Field Museum
‘The very first specimen that the Field Museum let me sample was Sue the T. rex. It was pretty nerve-wracking, since it’s such a famous fossil,’ said Dr Cullen.
Sue — so named after its discoverer, the explorer Sue Hendrickson — is formerly known as FMNH PR 2081. Its skeleton is around 90 per cent complete.
Dr Cullen used a special diamond-tipped drill to core a tiny cylinder — the size of a small battery — out of Sue’s thigh bone.
The resulting sample formed a cross-section of the bone, with the tree-ring-like lines showing where and how it had grown across the years of its life.
The missing piece in the thigh bone was then filled in with brown putty — although visitors to Sue’s exhibit at the Field Museum may just be able to see the repair if they look at the remains carefully.
In the lab, Dr Cullen and colleagues sliced samples of the bone core so thin that light could pass through them, allowing them to be examined under a microscope.
Under such a view, every tiny detail was revealed — including the spaces once occupied by blood vessels and bone cells that look like dots of black pepper.
‘The very first specimen that the Field Museum let me sample was Sue the T. Rex. It was pretty nerve-wracking, since it’s such a famous fossil,’ said Dr Cullen, who used a diamond-tipped drill to core a tiny cylinder — the size of a small battery — out of Sue’s thigh bone, pictured
‘Most animals have a period every year when they stop growing, traditionally suggested to be in times like winter when food is more scarce,’ said Dr Cullen.
‘It shows up in the bones as a line, like a tree ring.’
By analysing these growth lines and examining the bones for new regions of growth, experts can get a rough estimate of an animal’s age and how much it grew every year. There are also clues in the bone structure.
‘You can see all the little areas where the bone cells have grown, and the structure of the blood vessels that passed through the bone,’ Dr Cullen explained.
‘These vascular canals tell you roughly how fast the bone was growing.’
‘If the canals are more organised, the bone was being laid down more slowly, and if the structure is chaotic, it grew more quickly.’
The resulting sample formed a cross-section of the bone, pictured, with the tree-ring-like lines showing where and how it had grown across the years of its life
T. rex and its relatives — the coelurosaurs — showed a period of extreme growth during adolescence, one which petered out once they reached adulthood.
Sue lived to be about 33 years old — making her the oldest T. rex currently known —but had reached her adult size by the age of 20, the researchers found.
‘She probably gained around 35–45 lbs a week — as a teenager,’ said Dr Cullen.
The tyrannosaurids more distant cousins, the allosauroids, could reach sizes almost as big, the team noted.
However, these giants grew slowly throughout their whole lives — meaning that it was the oldest individuals that reached the largest sizes.
One allosauroid specimen that they sampled was a new carcharodontosaur from Argentina which had reached a size close to that of Sue, but not until its 30s–40s.
This dinosaur lived to be around 50 years old, making it the oldest individual theropod on record — aside from some modern birds like parrots.
Despite its advanced age, the carcharodontosaur appeared to have only stopped growing about two-to-three years before it became part of the fossil record.
T. rex and its relatives — the coelurosaurs — showed a period of extreme growth during adolescence, one which petered out once they reached adulthood. Pictured, the growth patterns of Sue (top) and other dinosaurs, with the number of growth lines (line of arrested growth, or ‘LAG’) on the bottom axis and the circumference on the side axis
The findings raise questions about how these predatory dinosaurs interacted with the animals around them.
The plant-eating dinosaurs that lived alongside T. rex were ceratopsians like Triceratops and duck-billed hadrosaurs.
They grew extremely quickly in adolescence too. The slow-growing allosauroid carnivores lived with big long-necked sauropods that also grew quickly, but appear to have taken a long time to reach full size. Those trends might be related.
‘There could be some kind of a selection pressure for the coelurosaurs to grow quickly to keep up with their prey, or pressure for the allosauroids to keep growing in size since their prey were also increasing in size,’ mused Dr Cullen.
‘It could be that even if the sauropods kept growing their whole lives, they had so many offspring that there was always something small to eat,’ he added.
The full findings of the study were published in the journal Proceedings of the Royal Society B.
KILLING OFF THE DINOSAURS: HOW A CITY-SIZED ASTEROID WIPED OUT 75 PER CENT OF ALL ANIMAL AND PLANT SPECIES
Around 65 million years ago non-avian dinosaurs were wiped out and more than half the world’s species were obliterated.
This mass extinction paved the way for the rise of mammals and the appearance of humans.
The Chicxulub asteroid is often cited as a potential cause of the Cretaceous-Paleogene extinction event.
The asteroid slammed into a shallow sea in what is now the Gulf of Mexico.
The collision released a huge dust and soot cloud that triggered global climate change, wiping out 75 per cent of all animal and plant species.
Researchers claim that the soot necessary for such a global catastrophe could only have come from a direct impact on rocks in shallow water around Mexico, which are especially rich in hydrocarbons.
Within 10 hours of the impact, a massive tsunami waved ripped through the Gulf coast, experts believe.
Around 65 million years ago non-avian dinosaurs were wiped out and more than half the world’s species were obliterated. The Chicxulub asteroid is often cited as a potential cause of the Cretaceous-Paleogene extinction event (stock image)
This caused earthquakes and landslides in areas as far as Argentina.
But while the waves and eruptions were The creatures living at the time were not just suffering from the waves – the heat was much worse.
While investigating the event researchers found small particles of rock and other debris that was shot into the air when the asteroid crashed.
Called spherules, these small particles covered the planet with a thick layer of soot.
Experts explain that losing the light from the sun caused a complete collapse in the aquatic system.
This is because the phytoplankton base of almost all aquatic food chains would have been eliminated.
It’s believed that the more than 180 million years of evolution that brought the world to the Cretaceous point was destroyed in less than the lifetime of a Tyrannosaurus rex, which is about 20 to 30 years.