THE popular image of dome-headed dinosaurs using their skulls as battering rams to fend off rivals may have to be revised. Pachycephalosaurs, or 鈥渢hick-headed dinosaurs鈥�, may not have been so hard-headed after all.
Pachycephalosaurs鈥� domed skulls were thought to have had a spongy radiating bone structure that seemed ideal for resisting compression forces. That led to the idea that the dinosaurs used their skulls as fighting weapons, just as mountain sheep use their horns today.
Now Mark Goodwin of the University of California at Berkeley and John Horner of Montana State University in Bozeman have re-examined seven skulls from juveniles and adults of closely related pachycephalosaur species. Thin sections of the bone viewed under the microscope showed that the radiating structures only existed in young pachycephalosaurs (Paleobiology, vol 30, p 253). They are 鈥渁bsent in adult skulls where this head-butting behaviour is presumed to have occurred鈥�, Goodwin says.
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But dense, highly variable, specialised fibres found within the outer layer of the dinosaur鈥檚 skulls suggest that the skull had a substantial external covering. 鈥淲e don鈥檛 even know what the final shape of the pachycephalosaur dome was,鈥� notes Goodwin. The researchers speculate that the ornament may have changed shape during life and been brightly coloured, acting as a visual signal similar to the frills of Triceratops or the horns of modern African cattle.