Dome-Headed Dinosaurs Fought Skull-Cracking, Head-Butting Battles, Fossils Show

Pachycephalosaurus wyomingensis

Offering a rare insight into specific — if somewhat self-destructive — dinosaur behavior, paleontologists say they think they’ve finally divined the purpose of the curious, bony crowns that once adorned a whole order of dome-headed dinosaurs.

They used them to butt heads — hard enough and often enough to frequently suffer skull trauma as a result, the scientists say.

Pachycephalosaurus wyomingensis
A dome-headed dinosaur, Pachycephalosaurus wyomingensis, with a skull lesion caused by head-butting (PLOS)

Writing in the journal PLoSOne, a team of researchers led by Dr. Joseph Peterson of the University of Wisconsin came to this conclusion after analyzing more than a hundred fossil skulls of pachycephalosaurids, a family of small, two-legged herbivores — all with thick protrusions on their foreheads — that once browsed the ancient West and parts of Asia.

After studying the domes of 109 separate dinosaurs of 14 different species, the scientists discovered what they describe as “a remarkably high incidence of cranial injury,” with many skulls pock-marked by lesions, or growths, that are typical signs of severe bone infections caused by trauma.

(Read about another recent dinosaur CSI investigation: “T. Rex Tooth Found in Dinosaur’s Tail Proves Tyrannosaurus Was a Predator“)

Twenty-four of the specimens from across 9 species — or 22% of the total sample — showed such signs of head injury.

And although pachycephalosaurs with flatter, smaller domes — which paleontologists believe were females and juveniles — were included in the study sample, none of them appeared to have suffered any trauma.

This suggests not only that head-butting was limited to adult males but also that — if modern animal behavior is any indication — it was likely used by them to fight over females.

Some scientists had previously theorized that the dinosaurs’ peculiar domes were sex characteristics intended to attract mates, like an elk’s antlers or a peacock’s tail feathers.

The new study intimates that the bony crests were meant not only to draw the eye but also to fight for the right to mate.

domehead dinosaurs fighting
Scientists (and artists) speculate that dome-headed dinosaurs might have battled in various ways that were comparable to modern animals: shoving each other like bison (a), clashing mightily like bighorn sheep (b) and swiping each other from the side, like goats (c) (PLOS)

“The pachycephalosaurian dome, therefore, and its remarkable history of injuries, hints at a rich, if conflict-filled, social life for these animals of which we still know little,” the scientists conclude.

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Sources:

• “Distributions of Cranial Pathologies Provide Evidence for Head-Butting in Dome-Headed Dinosaur,” PLoSOne, July 16, 2013

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