Working out how an extinct animal behaved when it was alive is tricky. But it is not always impossible, as Joseph Peterson and Collin Dischler of the University of Wisconsin explained on October 17th to the Society of Vertebrate Palaeontology meeting held in Raleigh, North Carolina. Pachycephalosaurs lived 65 million years ago. As their name suggests, they had large, bony, domed or round heads. For years, it was assumed they used these to attack one another in the way that
rams
(公羊) do now. Recently, though, a second suggestion has surfaced—that rather than for fighting, the domes were for show; the dinosaur equivalent of a peacock"s tail. Dr. Peterson and Dr. Dischler put these two theories into a head-to-head competition. To do so, they studied 102 pachycephalosaur bones, of various species. They found that 23 of these bones had pits in them, and that these pits were similar both to each other and to those found in the bones of living animals that attack each other with their heads. That supported the head-butting theory.
The clincher, though, came when they created computerised models of pachycephalosaur bones and mapped the damage from each of their pitted specimens on to these virtual bones. When they did this, they found that the pits were clustered—exactly as might be expected if they were the result of animals deliberately aiming at each other. Intriguingly, they found two patterns of clustering. Those pachycephalosaurs with highly domed heads had pits on both the fronts and the backs of their bones. Those whose domes were lower had them only on the fronts. This suggests the two sorts of animal fought in different ways. Low-domes, it seems, simply charged at each other. High-domes did that too. But they also engaged in head-to-head wrestling of a sort that allowed them to get behind their opponents" bones and do damage from the rear, in the way that modem bison do. None of which proves that pachycephalosaurs did not show off their stuff with their domes as well, just as a stag will often show off its antlers before engaging in combat, in order to give a less well-endowed rival the opportunity to withdraw.
But it does demonstrate that the domes were serious weapons, not mere showy clothing of fashion. How do scientists do with two different kinds of sayings of the pachycephalosaur"s dome
A．They insist on their own opinion of the pachycephalosaur"s dome. B．They study both of the theory with equal weight. C．They give up both of the sayings. D．They do not care much about the sayings at all.