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Why Did The Stegoceras Dinosaur Have A Domed Head?

At six feet in length, this two legged plant eater was about the size of a large dog with a strange domed head.

Stegoceras

Photo: Paul (Flickr)

Scientists are studying why the Stegoceras had a domed head.

Stegoceras validum is one of several dinosaur species with dome shaped skulls and is the subject of much debate. The big question is: what was its dome used for?

Why A Dome?

Stegoceras roamed North America seventy five to nearly eighty million years ago. At six feet in length, this two legged plant eater was about the size of a large dog. Its skeleton is unremarkable, except for the skull which looks like it’s equipped with a natural bicycle helmet. It’s not surprising that early paleontologists thought the dome might have been a battering ram. But was that the case?

Domes might have been used for head butting competitions between males. But domes could also have been used to get rid of body heat, or have been colorful mate attractors, like peacock’s tails. Or maybe domes were simply used to signal species’ identity in visual communication. Without a time machine to find out for sure, scientists are looking at fossils for clues.

CT Scans

Using a CT scanner, some scientists studied Stegoceras fossils to see how the skull was constructed. Head butting mammals have a stiff bone on the skull’s outside with a hollow but strong, spongy bone layer beneath that acts as a shock absorber. A third bone layer protects the brain. Stegoceras had something similar, but does that mean it was head butting with its dome?

Other scientists studying Stegoceras fossils think not. If males used their domes for head butting competitions, adults would be expected to have the most developed spongy layer.

Instead, scientists found that juveniles had the largest spongy layers, older adults the smallest. This suggests that domes might have been a product of a fast growth in juveniles and not a head butting feature. Scientists hope to find more fossils that will give them additional evidence. Until then, the dome remains a mystery.

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