Fossils Reveal Headbutts May Have Been Used as a Dinosaur Courtship Behavior

Pachycephalosaurids could attack each other with their dome-shaped skulls in a variety of ways. Credit: Ryan Steiskal

Pachycephalosaurids had domed heads with thick, bony protuberances, which paleontologists hypothesized the dinosaurs used in courtship behavior, perhaps to determine which male would be allowed to mate. A new study indicates that these dinosaurs might have been bashing themselves in a number of different ways.

The scientists presented their findings at the Society of Vertebrate Paleontology’s annual meeting in Raleigh, North Carolina. Initially, paleontologists were looking at the dome of a Pachycephalosaurus wyomingensis fossil, and noticed lesions that appeared to stem from injuries. They looked at 102 domes from fossil collections around the world. Of those, 23 had lesions. They produced a 3D model of  P. wyomingensis‘ skull and mapped the injuries.

Pachycephalosaurus wyomingensis skeleton, image by David Tana

The shape of the dome differed from fossil to fossil, and the placement of the injuries depended on the shape of the skull. Some skulls had injuries to the front, while others had injuries distributed between the front and back. This implied that P. wyomingensis with differently shaped skulls were bumping their heads in different ways.

These lesions were similar to those often seen in modern mammals. Bighorn sheep (Ovis canadensis) charge each other head on. Mountain goats (Oreamos americanus) bump each other in the flanks and bison (Bison bison) wrestle each other with their horns. Based upon these modern-day examples, the scientists speculated that the high-domed P. wyomingensis with parietal injuries were side-bumping like mountain goats, and the frontal injuries indicate bison-like wrestling.

This could be due to different species bashing in different ways, or a single species where juveniles and adults exhibit different behavior. There still is skepticism about whether the lesions are impressions of head-butting. The skulls could have been chipped after death. A look at the skull bone microstructure will determine if the lesion sites suffered trauma.