The findings highlight the possible link between climate and the evolution of these prehistoric animals

Distinct from their closest reptilian cousins like crocodiles, Dinosaurs evolved the ability to regulate their body temperature. How these adaptations appeared, and when, are two unanswered questions in dinosaur evolution. An international article led by Alfio Chiarenza and Sara Varela, published today in the journal Current Biology provides some answers to these questions.

Thermoregulation is an important biological feature inherited by the only group of living dinosaurs– birds–placing them among the most adaptable animals on our planet today. The ability of some dinosaurs to live and nest in cold polar regions raises intriguing questions about the origins of their warm-bloodedness. It indicates that homeothermy (keeping a constant body temperature) and endothermy (generating body heat) must have evolved, at least, in two groups of dinosaurs inhabiting those harsher environments: the plant-eating ornithischians (which include Stegosaurus and Triceratops) and the mostly carnivorous theropods (like Tyrannosaurus rex and Velociraptor), which also include birds.

In our study published today in the journal Current Biology, by combining fossils with phylogenetic trees and palaeoclimatic models, we show that ornithischians and theropods diversified across a wide suite of climates, also occupying colder environments, while the long-necked herbivorous sauropodomorphs exhibited prolonged climatic conservatism associated with warmer environments. This suggests that the latter maintained a cold-blooded physiology more strongly dependent on higher external temperatures.

Moreover, our analyses show that the divergence in dinosaurs’ climatic preferences coincided with the so-called ‘Jenkyns’ event, an Early Jurassic episode (~ 183 million years ago) of global warming that was followed by the diversification of many dinosaur lineages, including the emergence of feathered dinosaurs. Further key changes in climatic preferences likely occurred during the Cretaceous Thermal Maximum, a later (~90 million years ago) excursion in temperature, supporting a critical role of adaptation during hyperthermal events in the geologic past.

Notably, these results provide novel insights into the origin of birds’ unique temperature regulation, suggesting that the evolution of their active metabolism likely started in the Early Jurassic, a crucial period for the evolution of small feathered dinosaurs. An active metabolism might have provided an advantage for speeding up the development of smaller- feathered species, who might have found it easier to survive than more primitive, large and slower-developing, ancestors in the wake of environmental crises like the Jenkyns event.

A link between climate and dinosaurs evolution

These findings highlight a potential link between climate and the evolution of dinosaurs, offering new clues on the dinosaurian origins of birds and the broad diversity of thermophysiological strategies adopted by Mesozoic dinosaurs. Our study contributes to a more nuanced understanding of dinosaurian evolution and the interplay between the planet and their diverse ecology.

The study involved researchers from the University College London, University of Vigo, the University of Bristol and the Museo Nacional de Ciencias Naturales in Madrid, and received funding from the European Research Council, the Spanish Ministry of Research the Natural Environment Research Council and The Royal Society.

Graphical abstract