Study: Warm-Bloodedness in Theropod and Ornithischian Dinosaurs Evolved by Early Jurassic | Sci.News

This artist's impression shows a dromaeosaur, a type of feathered theropod, in the snow. Image credit: Davide Bonadonna / Universidade de Vigo / UCL.

In the early 20th century, dinosaurs were considered slow-moving, cold-blooded animals like modern-day reptiles, relying on heat from the Sun to regulate their temperature.

Newer discoveries indicate some dinosaur types were likely capable of generating their own body heat but when this adaptation occurred is unknown.

In the new study, University College London paleontologist Alfio Alessandro Chiarenza and colleagues looked at the spread of dinosaurs across different climates on Earth throughout the Mesozoic Era, drawing on 1,000 fossils, climate models and the geography of the period, and dinosaurs' evolutionary trees.

The researchers found that two of the three main groupings of dinosaurs, theropods (such as T. rex and Velociraptor) and ornithischians (including relatives of the plant eaters Stegosaurus and Triceratops), moved to colder climates during the Early Jurassic, suggesting they may have developed endothermy (the ability to internally generate heat) at this time.

In contrast, sauropods, the other main grouping which includes Brontosaurus and Diplodocus, kept to warmer areas of the planet.

Previous research has found traits linked to warm-bloodedness among ornithischians and theropods, with some known to have had feathers or proto-feathers, insulating internal heat.

"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," Dr. Chiarenza said.

"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."

"Theropods also include birds and our study suggests that birds' unique temperature regulation may have had its origin in this Early Jurassic epoch," said Dr. Sara Varela, a paleontologist at the Universidade de Vigo.

"Sauropods, on the other hand, which stayed in warmer climates, grew to a gigantic size at around this time — another possible adaptation due to environmental pressure."

"Their smaller surface area to volume ratio would have meant these larger creatures would lose heat at a reduced rate, allowing them to stay active for longer."

In the study, the scientists also investigated if sauropods might have stayed at lower latitudes to eat richer foliage unavailable in colder polar regions.

Instead, they found sauropods seemed to thrive in arid, savannah-like environments, supporting the idea that their restriction to warmer climates was more related to higher temperature and then to a more cold-blooded physiology.

During that time, polar regions were warmer, with abundant vegetation.

The Jenkyns event occurred after lava and volcanic gasses erupted from long fissures in the Earth's surface, covering large areas of the planet.

"This research suggests a close connection between climate and how dinosaurs evolved," said Dr. Juan Cantalapiedra, a paleontologist at the Museo Nacional de Ciencias Naturales.

"It sheds new light on how birds might have inherited a unique biological trait from dinosaur ancestors and the different ways dinosaurs adapted to complex and long-term environmental changes."

The findings were published in the journal Current Biology.

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Alfio Alessandro Chiarenza et al. Early Jurassic origin of avian endothermy and thermophysiological diversity in dinosaurs. Current Biology, published online May 15, 2024; doi: 10.1016/j.cub.2024.04.051