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

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.
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.

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