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

Published online by Cambridge University Press:  08 February 2016

Mark B. Goodwin  and
John R. Horner
Mark B. Goodwin
Affiliation:
Museum of Paleontology, University of California, Berkeley, California 94720 and Department of Geology, University of California, Davis, California 95616. E-mail: [email protected]
John R. Horner
Affiliation:
Museum of the Rockies, Montana State University, Bozeman, Montana 59717. E-mail: [email protected]
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Abstract

Modern histological techniques allow paleontologists to investigate the internal microstructure of bone tissue. We apply high resolution images of histological thin sections from an ontogenetic series (not conspecific) of pachycephalosaurid frontoparietal domes to test the hypothesis that these Late Cretaceous dinosaurs used their heads as battering rams, analogous to the behavior of 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.

Type
Articles
Information
Paleobiology , Volume 30 , Issue 2 , Spring 2004 , pp. 253 - 267
Copyright
Copyright © The Paleontological Society 

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