Dinosaurs Needed to Be Cold Enough for Warm Blood to Matter

Enlarge / Later theropods had multiple adaptations to varying temperatures.

Dinosaurs were once assumed to be ectothermic or cold-blooded, an idea that makes sense given that they were reptiles. While scientists had previously discovered evidence of warm-blooded dinosaur species, it is still unknown what could have triggered this adaptation. A team of researchers now thinks that dinosaurs that already had some tolerance for cold developed endothermy, or warm blood, to adapt when they migrated to regions with colder temperatures. They also believe they have found a possible reason for the trip.

Using the Mesozoic fossil record, evolutionary trees, climate models and geography, as well as taking into account a drastic climate change event that caused global warming, the team found that theropods (predators and ancestors of birds such as velociraptor and T . rex) and ornithischians (such as triceratops and stegosaurus) must have reached colder regions during the Early Jurassic. The lower temperatures are thought to have selected for species that were partially adapted to endothermy.

“The early invasion of interesting niches… [suggests] an early achievement of homeothermic (possibly endothermic) physiology in [certain species]allowing them to colonize and persist even at extreme latitudes since the Early Jurassic,” the researchers said in a study recently published in Current Biology.

hot real estate

During the Mesozoic Era, which lasted from 230 to 66 million years ago, protodinosaurs known as dinosauromorphs began to diversify in hot, dry climates. Early sauropods, ornithischians, and theropods tended to remain in these regions.

Sauropods (such as brontosauruses and diplodocus) would become the only groups of dinosaurs that would enjoy the heat; The fossil record shows that sauropods tended to stay in warmer areas, even if there was less food. This suggests the need for sunlight and heat associated with ectothermy. According to one hypothesis, they might have been able to survive in colder temperatures, but not be adapted enough to survive for long.

It’s also possible that living in colder areas meant too much competition with other types of dinosaurs, as theropods and ornithischs ended up moving to these colder areas.

Almost apocalypse

Beyond the ecological opportunities that may have attracted dinosaurs to colder territories, it is possible that they were driven out of warm territories. About 183 million years ago, there was a disturbance in the carbon cycle, along with extreme volcanism that spewed out huge amounts of methane, sulfur dioxide and mercury. Life on Earth was affected by scorching heat, acid rain, and forest fires. Known as the Early Jurassic Jenkyns Event, researchers now think that these disturbances pushed theropod and ornithischian dinosaurs into colder climates because temperatures in warmer areas exceeded the optimal temperatures for their survival.

Theropods and ornithischians that escaped the effects of the Jenkyns event may have had a key adaptation to colder climates; It is now believed that many dinosaurs in these groups had feathers. Feathers can be used to both trap and release heat, which would have allowed feathered dinosaurs to regulate their body temperature in more diverse climates. Modern birds use their feathers in the same way.

Dinosaur species with feathers or special structures that improved heat management might have been homeothermic, meaning they would have been able to maintain their body temperature with metabolic or even endothermic activity.

Beyond dinosaurs migrating to high latitudes and adapting to falling temperatures, endothermy could have led to the emergence of new dinosaur species and lineages. It could have contributed to the rise of Avialae, the clade that includes birds (the only real dinosaurs still in existence) and can be traced back to their earliest ancestors.

“[Our findings] “They provide novel insights into the origin of avian endothermy, suggesting that this evolutionary trajectory within theropods…likely began in the late Early Jurassic,” the researchers said in the same study.

It’s really something to think about the next time a sparrow passes by.

Current Biology, 2024. DOI: 10.1016/j.cub.2024.04.051

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