Giant sauropod dinosaurs such as Brontosaurus and Diplodocus preferred to live in warmer, more tropical regions of Earth, according to a new study.
The findings suggest the long-necked animals, thought to include the largest land animals to have ever existed, may have had a different physiology from other dinosaurs.
Researchers at UCL and the University of Vigo investigated why sauropod fossils are only found at lower latitudes, while fossils of other main dinosaur types seem to be present everywhere, with many located in the polar regions.
They analysed the fossil record across the Mesozoic era, lasting from around 230 to 66 million years ago, looking at occurrences of fossils of the three main dinosaur types.
This included sauropods, theropods – which include velociraptors and Tyrannosaurus rex – and ornithischians such as the Triceratops.
Combining this data with information about climate throughout the period, and data about how continents have moved across the globe, the researchers concluded that sauropods were restricted to warmer, drier habitats compared with other dinosaurs.
These habitats were likely to be open, semi-arid landscapes, similar to today’s savannahs.
Co-author Dr Philip Mannion, UCL Earth Sciences, said: “Our research shows that some parts of the planet always seemed to be too cold for sauropods.
“They seem to have avoided any temperatures approaching freezing.
“Other dinosaur types, in contrast, could thrive in Earth’s polar regions, from innermost Antarctica to polar Alaska – which, due to the warmer climate, were ice-free, with lush vegetation.
“This suggests sauropods had different thermal requirements from other dinosaurs, relying more on their external environment to heat their bodies – slightly closer to being ‘cold-blooded’, like modern-day reptiles.
“Their grand size hints that this physiology may have been unique.”
First author Dr Alfio Alessandro Chiarenza, previously at UCL and now based at the University of Vigo, Spain, said: “It may be that sauropods were physiologically incapable of thriving in colder regions, or that they thrived less well in these areas than their dinosaurian cousins and were outcompeted.
“A mix of features may have helped sauropods shed heat more easily than mammals do today.
“Their long necks and tails would have given them a larger surface area, and they may have had a respiratory system more akin to birds, which is much more efficient.”
He added: “Sauropods’ strategies for keeping their eggs warm may also have differed from the other dinosaurs.
“Theropods probably warmed eggs by sitting on them, whereas ornithischians seem to have used heat generated by decaying plants.
“Sauropods, meanwhile, may have buried their eggs, relying on heat from the sun and the ground.”
The study found no occurrences of sauropods above a latitude of 50 degrees north – an area encompassing most of Canada, Russia, northern Europe and the UK – or below 65 degrees south, encompassing Antarctica.
But there were rich records for theropods and ornithischians living above 50 degrees north in later periods (from 145 million years ago).
The authors also suggest sauropods may have had a unique in-between physiology, closer to being cold-blooded than other dinosaur types.
The findings are published in Current Biology.