Anyone who grew up watching Jurassic Park might think of Tyrannosaurus Rex as a clumsy, cold-blooded killer.
But while the T.Rex hasn’t been friendly, scientists now say the ‘King of the Dinosaurs’ may not have actually been cold-blooded.
An international team of researchers says the ability to generate body heat like modern birds and mammals may have first evolved 180 million years ago.
They found that two of the main groups of dinosaurs moved towards colder climates during the Early Jurassic period, suggesting they could warm up.
Co-author Dr. Juan Cantalapiedra, from the National Museum of Natural Sciences in Madrid, says this finding “sheds new light on how birds could have inherited a unique biological trait from the ancestors of dinosaurs.”
Scientists say the T.Rex belongs to a family of dinosaurs that may have developed the ability to generate its own body heat about 180 million years ago.
For most of the 20th century, dinosaurs were still thought to be large, cumbersome reptiles.
Scientists believed that dinosaurs would have needed to warm themselves in the sun, just like today’s lizards and snakes.
But much of what scientists have learned about dinosaurs since then defies these expectations.
In particular, scientists now know that many dinosaurs actually had layers of feathers or protofeathers that would have been excellent for keeping warm.
This suggests that some dinosaurs may have developed the ability to produce their own heat, known as endothermy, making them warm-blooded animals like birds and mammals are today.
To unravel the story of how this ability might have evolved, scientists compared 1,000 fossils to a model of the prehistoric climate of the place where they were discovered.
Researchers say the feathered relatives of the T.Rex and Velociraptor spread to colder regions to survive a climate disaster and evolved the ability to regulate their own internal temperature. This art print shows a dromaeosaur, a type of feathered theropod, in the snow.
This graph shows how many fossils of the three main groups of dinosaurs were found in different climates. You can see how the number of Theropods and Ornithischians found in cold climates (purple) increases over time
Dinosaurs can be divided into three main groups: theropods such as T.Rex and Velociraptor, ornithischians, which include relatives of Stegosaurus and Triceratops, and sauropods such as Diplodocus and Brontosaurus.
The researchers found that theropods and ornithischians spread into colder, wetter climates during the Early Jurassic period, while sauropods remained in warmer regions.
The researchers propose that theropods and ornithischians were able to perform this movement because they had developed the ability to regulate their own temperature.
First author Dr Alfio Chiarenza, a palaeontologist at UCL, said: “Our analyzes show that different climate preferences emerged among major dinosaur groups around the time of the Jenkyns event, 183 million years ago.”
“The adoption of endothermy, perhaps as a result of this environmental crisis, may have allowed theropods and ornithischians to thrive in colder environments.”
This graph shows the evolution of theropods, the ancestors of modern birds, in relation to the temperature of their habitat. You can see how more dinosaurs adapted to living in colder climates (below on the graph) as they evolved.
Sauropods, which include dinosaurs such as Diplodocus (pictured), remained in warmer climates and may have grown to their enormous size to help conserve heat.
The catalyst for this sudden change may have been a mass extinction called the Jenkyns event, in which vast volcanic fissures covered much of the planet with lava and gases.
This caused global temperatures to rise suddenly, driving many plant and dinosaur species to extinction.
Dr. Chiarenza says endothermy may have allowed dinosaurs like Velociraptor and T.Rex to remain active for longer periods of time, develop faster and have more offspring.
After the Jenkyns event, sauropods that remained in warmer climates grew to enormous size, and dinosaurs such as Diplodocus reached 28 m (92 ft) in length.
Theropods like Velociraptor (pictured) are some of the earliest ancestors of modern birds. Researchers say this suggests the birds’ warm-blooded nature could have evolved 180 million years ago.
Researchers say this is also evidence of intense environmental pressures.
Co-author Dr Sara Varela, from the University of Vigo, says: “Their lower surface-to-volume ratio would have meant that these larger creatures would lose heat at a reduced rate, allowing them to remain active for longer.”
In addition to debunking another dinosaur myth, this study may also provide insight into the evolutionary history of modern animals.
All modern birds are warm-blooded and can be found everywhere from deserts to the coldest polar regions.
Meanwhile, cold-blooded animals like lizards and snakes still tend to be found only in warmer parts of the world.
