Blood vessels in their heads kept big dinos from overheating

The ancient giants evolved different ways for cooling their blood

The long-necked giant Diplodocus (illustrated) may have panted to keep its blood cool (veins are in blue, arteries in red) and to avoid heatstroke.

Life restoration by Michael Skrepnick. Courtesy of WitmerLab at Ohio University

Massive dinosaurs came in many different forms. All, it turns out, had the same problem of staying cool. Now, scientists have analyzed fossilized traces of blood vessels in the skulls of big-bodied dinos. This revealed how the giants had avoided heatstroke.

Earlier research has suggested that some large dinos had body temperatures similar to modern mammals. Somehow, massive, long-necked sauropod dinosaurs kept their bodies between 36º and 38º Celsius (96.8º and 100.4º Fahrenheit). This range is cooler than birds but warmer than crocodiles.

One possible explanation for how they managed this was thermoregulation. This process allows an organism to keep its own body temperature under control. Dinosaurs may have done this by releasing excess heat from their blood vessels.

One type of thermoregulation is called evaporative cooling. That’s when liquid water evaporates from a surface, such as the skin. This process helps heat escape by cooling the skin’s temperature. This process could have occurred in moist parts of a dino’s body, such as its nose and mouth.

Wm. Ruger Porter and Lawrence M. Witmer are vertebrate paleontologists. That means they study ancient animals with backbones. Both work at the Ohio Center for Ecology and Evolutionary Studies in Athens. The two mapped networks of dino blood vessels in fossil skulls. To do this, they performed CT scans of the skulls. They did the same thing with skulls from birds and reptiles, the dinos’ modern kin.

CT scans combine X-rays to create 3-D images of internal structures. Those images let the scientists map blood vessels in the ancient animals. Their goal was to figure out how dinosaurs might have controlled their body temperature.

Dinosaurs each evolved their own ways to beat the heat, these scans showed. The team reported its findings October 16 in The Anatomical Record.

Large, armor-covered ankylosaurs had blood vessels in their noses. These were cooling regions. The enormous, long-necked sauropods, such as Diplodocus, also had blood vessels clusters in their nostrils and mouths. This suggests that they used panting to stay cool, Porter and Witmer say. And large theropods like Tyrannosaurs rex 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 those sinus passages.

Carolyn Gramling is the earth & climate writer. She has bachelor’s degrees in geology and European history and a Ph.D. in marine geochemistry from MIT and the Woods Hole Oceanographic Institution.

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