Big dinosaurs kept cool thanks to blood vessel clusters in their heads

Massive dinosaurs came in many different forms, but they all had the same problem: Staying cool. Now, fossilized traces of blood vessels in the skulls of big-bodied dinosaurs reveal how different dinos avoided heatstroke. Long-necked sauropods may have panted to stay cool, for example, while heavily armored ankylosaurs relied on elaborate nasal passages.

Chemical analyses of fossil sauropod teeth previously suggested that, despite their massive bodies, the animals maintained body temperatures similar to those of modern mammals (SN: 6/23/11). One possible explanation for this was thermoregulation, in which blood vessels radiate excess heat, often with the help of evaporative cooling in moist parts of the body, such as the nose and mouth.

To assess how giant dinosaurs might have used thermoregulation, two vertebrate paleontologists from the Ohio Center for Ecology and Evolutionary Studies in Athens mapped blood vessel networks within fossil dinosaur skulls and skulls from dinosaurs’ modern relatives, birds and reptiles. The researchers traced the networks in the bones using computed tomography scanning that combines X-rays into 3-D images. Along with data and observations from the modern relatives, those images let the scientists map blood vessel patterns in the ancient animals. Dinosaurs from Diplodocus to Tyrannosaurus rex each evolved their own ways to beat the heat, the team reports October 16 in The Anatomical Record.

Ankylosaurs had thick clusters of blood vessels, representing cooling regions, primarily in their noses. Sauropods had blood vessels clusters in their giant nostrils and mouths, suggesting they used panting to stay cool. And fierce, large theropods like T. rex and Allosaurus may have used their sinuses. An extra air cavity connected to their jaw muscles was also rich in blood vessels, the team found. Opening and closing their jaws would have pumped air in and out of the sinus like a bellows.