First warm-blooded dinosaurs adapted to cool climates

The first dinosaurs to have a warm-blooded metabolism might have emerged 180 million years ago during the early Jurassic period, according to a new study.

Warm-bloodedness, or endothermy, is a trait that is now common to all modern mammals and birds. Now that we know dinosaurs are the ancestors of birds, it stands to reason that at least some dinosaurs were also warm-blooded.

This was first argued by palaeontologist Robert Bakker. In his 1968 book, The Superiority of Dinosaurs, Bakker challenged the notion of dinosaurs as slow-moving, cold-blooded monsters. Instead, he said they were “fast, agile, energetic creatures.”

Debate has raged since then about the metabolism of the dinosaurs.

A 2022 study used chemical analysis of dinosaur fossils to show that most dinosaur groups – including the two-legged theropods and the long-necked sauropods – were warm-blooded.

So, when did endothermy evolve in dinosaurs?

New research published in the journal Current Biology might have answered that question.

The researchers looked at the spread of dinosaurs across different climates during the Mesozoic Era (230–66 million years ago).  The work drew on 1,000 fossils, models of climate and geography of the period, and evolutionary trees for dinosaurs.

They found 2 of the 3 main dinosaur groups – theropods like Tyrannousaurus rex and Velociraptor, and ornithischians like Stegosaurus and Triceratops – moved to colder climates during the Early Jurassic (roughly 201–175 million years ago). This suggests the animals had developed endothermy, making them more able to withstand colder environments.

Warm-bloodedness has been hinted in both groups, including the discovery of fossil feathers for heat retention.

Meanwhile, sauropods kept to warmer parts of the planet.

“Our analyses show that different climate preferences emerged among the main dinosaur groups around the time of the Jenkyns event 183 million years ago, when intense volcanic activity led to global warming and extinction of plant groups,” says first author Dr Alfio Alessandro Chiarenza from University College London, UK.

“At this time, many new dinosaur groups emerged. The adoption of endothermy, perhaps a result of this environmental crisis, may have enabled theropods and ornithischians to thrive in colder environments, allowing them to be highly active and sustain activity over longer periods, to develop and grow faster and produce more offspring.”

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