Dinosaur Evolution: From Cold to Warm-Blooded in Cooler Climates

Dinosaurs were once thought to be ectothermic, or cold-blooded, which seemed plausible given their reptilian nature. However, recent evidence suggests that some dinosaur species were warm-blooded, and researchers are now proposing a reason for this adaptation. A team of scientists hypothesizes that dinosaurs with some cold tolerance evolved endothermy, or warm-bloodedness, as they migrated to regions with cooler temperatures during the Early Jurassic period. They also believe they’ve identified a potential trigger for this migration.

By analyzing Mesozoic fossils, evolutionary trees, climate models, and geography, the team found evidence that theropods (predators and bird ancestors like velociraptor and T. rex) and ornithischians (such as triceratops and stegosaurus) moved to colder regions early in their history. These lower temperatures likely favored species partly adapted to endothermy.

“The early occupation of cooler niches… [suggests] an early adoption of homeothermic (possibly endothermic) physiology in certain species, enabling them to colonize and survive in extreme latitudes since the Early Jurassic,” the researchers reported in a study published in Current Biology.

During the Mesozoic Era, which spanned from 230 to 66 million years ago, early sauropods, ornithischians, and theropods thrived in hot, dry climates. Sauropods like brontosaurus and diplodocus tended to stay in warmer areas, suggesting they relied on sunlight and heat, characteristics associated with ectothermy. These sauropods may have been capable of surviving in colder temperatures but were not well adapted for long-term residence, according to one hypothesis.

Competitive pressure or ecological changes may have driven theropods and ornithischians into cooler regions. Around 183 million years ago, a disruption in the carbon cycle and extensive volcanic activity triggered the Early Jurassic Jenkyns Event, resulting in extreme heat, acid rain, and wildfires. This environmental upheaval may have forced these dinosaurs to migrate to cooler climates.

The theropods and ornithischians that survived the Jenkyns Event possibly had adaptations suited to cooler climates, such as feathers, which can trap and release heat. This feature allowed feathered dinosaurs to regulate their body temperature across diverse environments, akin to modern birds.

Species with feathers or similar adaptations were likely homeothermic, capable of maintaining their body temperature through metabolic activity or even endothermy.

Beyond migration to cooler latitudes, endothermy could have spurred the evolution of new dinosaur species and lineages. It may have played a crucial role in the rise of Avialae, the clade that includes modern birds and traces its lineage back to early dinosaur ancestors.

“Our findings provide new insights into the origin of avian endothermy, suggesting that this evolutionary path within theropods likely began in the latest Early Jurassic,” the researchers concluded in their study.

Next time a sparrow flies by, consider its origins in a lineage that dates back to the dinosaurs.