Sunday, July 21, 2013

Headbutts or headdresses

Pachycephalosaurs were a group of dinosaurs with a distinctive feature: a thick dome on the head, usually fringed with small spikes (RECONSTRUCTION ABOVE BY RYAN STEISKALW, PHOTOGRAPHS OF SKULLS HERE). Some paleontologists believe that the protective skulls were used by the animals as battering rams, allowing them to charge each other over mates and/or territories. Others contend that the dome was too brittle to withstand the impact and was instead intended to attract mates or identify it to members of their own species. Fossils have telltale damage, but scientists had assumed it occurred postmortem through erosion or by scavengers. Except that the scarring was always found in the same place on the dome of the skull, suggesting the dinosaurs did butt heads like rams. Joseph Peterson of the University of Wisconsin decided to do a survey. He and his colleagues spent 5 years studying 14 species of pachycephalosaurs – a total of 109 skulls. They found healed fractures and thick, irregular surfaces that indicated past infection and inflammation on 22% of them. The damage was not present on the flatter domes which probably belonged to females or youngsters, suggesting that the charging behavior was only done by the males. Still, there are other theories, for instance that the ramming was done head-to-flank rather than head-to-head. So the scientists have agreed to disagree, but Peterson allows that their strangely-shaped heads may have been both a billboard of their prowess and a weapon. "I think that the idea of the domes being used as a display structure is very likely. A display structure is great for communicating about how tough animals are… but sometimes they have to back that up.”

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