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Re: Pachycephalosaurs & head-butting

Cranial histology of pachycephalosaurs (Ornithischia:Marginocephalia) reveals transitory structures inconsistent with head-butting behavior

Mark B. Goodwin and John R. Horner Paleobiology, 30(2), 2004, pp. 253-267

Abstract.-Modern histological techniques allow paleontologists to investigate the internal microstructureof bone tissue. We apply high resolution images of histological thin sections from an ontogeneticseries (not conspecific) of pachycephalosaurid frontoparietal domes to test the hypothesis that these Late Cretaceous dinosaurs used their heads as battering rams, analogous to the behaviorof the bighorn sheep, Ovis canadensis, or as a thermoregulatory device. Our analysis reveals that the internal structure of the pachycephalosaur dome is a dynamic tissue that reflects the changeable expansion and vascularity of the dome throughout ontogeny. The radiating structures within the frontoparietal dome, used previously to support ''head-butting'' hypotheses, are unexpectedly transitory, diminishing in mature individuals and nearly absent in adult skulls where head-butting behavior is presumed to occur. The unique architecture of the pachycephalosaurid dome is dividable into three distinct Zones. We demonstrate that the relative vascularity, associated tissue structures, and orientation and density of Sharpey's fibers within these Zones are modified during growth. Evidence for an external dome covering in vivo precludes the determination of the final shape of the pachycephalosaur skull. On the basis of these new observations, we propose that cranial display in support of species recognition and communication is a more parsimonious interpretation of the function of the pachycephalosaurid dome. Sexual display behaviors were probably secondary.

----- Original Message ----- From: <hammeris1@bellsouth.net>
To: <dinosaur@usc.edu>
Sent: Wednesday, April 02, 2008 3:48 AM
Subject: Pachycephalosaurs & head-butting

I thought I've read recent conclusions that their bony-skull tops were far too thin to support this activity?