T. rex was bigger than thought: study

Tuesday, August 4, 2015

The iconic T. rex dinosaur grew bigger and faster than previously estimated, according to British and US scientists.

Scientists digitally modelled flesh on five mounted T. rex skeletons and showed that the meat-eating lizard kings were up to a third bigger and grew two times as fast into adults than previous research had suggested.

The findings, led by Professor John Hutchinson of The Royal Veterinary College, London, and Peter Makovicky, curator of dinosaurs at The Field Museum of Natural History in Chicago, are published in the journal PloS One .

One of the skeletons included in the study was "Sue", the largest and most complete T. rex specimen ever found, on display at The Field Museum.

The 67-million-year-old dinosaur was discovered in 1990 on an Indian reservation in South Dakota by American palaeontologist Sue Hendrickson.

Named after its finder, Sue was previously thought to be about the size of a big elephant or rhinoceros, standing 3.5 metres high and 13 metres from head to tail.

Her living weight was guessed to be 6400 kilograms, or about six and a half tonnes.

But the latest methods found she would have tipped the scales at well over nine tonnes.

"We knew she was big but the 30 per cent increase in her weight was unexpected," says Makovicky.

Using digital models

The technique used mounted skeletons to derive body mass estimates, instead of models created to scale.

The team made three-dimensional laser scans of the skeletons to form a template for digital models that would add simulated flesh.

They devised three different levels of the approximate amount of flesh the creatures likely had, to figure the size of a thin, hungry animal up to a well-fed one.

"Previous methods for calculating mass relied on scale models, which can magnify even minor errors, or on extrapolations from living animals with very different body plans from dinosaurs," says Makovicky.

"We overcame such problems by using the actual skeletons as a starting point for our study."

By establishing new sizes for the other four specimens studied, the researchers also found that the creatures likely grew faster than initially thought.

"We estimate they grew as fast as 1790 kilograms per year during the teenage period of growth, which is more than twice the previous estimate," says lead author Hutchinson.

That would mean the land-roaming carnivores expanded by about 5 kilograms per day during their peak growth spurt, more than double their 2004 estimate of 2.1 kilograms per day.

T.rex's serrated teeth tore through flesh

An artist's impression of Gorgosaurus, a cousin of T.rex, ripping apart another dinosaur with its serrated teeth (Danielle Dufault)

Will Dunham

If you want to know the secret behind the success of Tyrannosaurus rex and its meat-eating dinosaur cousins, look no further than their teeth.
A comprehensive analysis of the teeth of the group of carnivorous dinosaurs called theropods, published in the journal Scientific Reports, details a unique serrated structure that let them chomp efficiently through the flesh and bones of large prey.

Theropods first appeared about 200 million years ago and were the dominant terrestrial meat-eaters until the age of non-avian dinosaurs ended about 65 million years ago.

The study involving eight theropod species revealed their previously unknown tooth complexity.
Internal dental tissues were arranged in a way that reinforced the strength and prolonged the life of teeth that were serrated like steak knives for easy dismembering of other dinosaurs.

Fossil evidence shows that T. rex's teeth could crush bone. Its teeth have been found embedded in the bones of its prey and chunks of bone appear in its fossilised dung, says the study's lead author palaeontologist Kirstin Brink of the University of Toronto Mississauga.

"But the serrations were most efficient for piercing flesh and gripping it while ripping off a chunk of meat, called the 'puncture and pull' feeding style," says Brink.

The researchers analysed slices from fossil teeth using a powerful microscope and a sophisticated device that revealed tooth chemical properties.

They studied teeth from: the early and relatively small Coelophysis; bird-like Troodon; large predators Allosaurus, Gorgosaurus, Daspletosaurus, Tyrannosaurus and Carcharodontosaurus; and big, semi-aquatic Spinosaurus.

The teeth of Tyrannosaurus and Carcharodontosaurus measured up to 23 centimetres long.
"In theropods, the serrations are larger and deeper than the superficial view suggests, making them stronger and longer lasting, less likely to get damaged or worn," says study co-author Professor Robert Reisz also of the University of Toronto Mississauga.

Dinosaurs were able to continuously grow teeth throughout their lives. When a tooth was broken, another could replace it.

"It could take up to two years for a tooth to grow back in the big theropods like T. rex. Therefore, having specially reinforced teeth means less tooth breakage and less gaps in the jaw, leading to more efficient eating," says Brink.

The Komodo dragon, an Indonesian lizard that grows up to three metres long, is the only living reptile with serrated teeth closely resembling those of theropods, although these teeth evolved independently of those of the dinosaurs, says Brink.