Abstract Citation: Horner JR, Goodwin MB (2009) Extreme Cranial Ontogeny in the Upper Cretaceous Dinosaur Pachycephalosaurus. PLoS ONE 4(10): e7626. doi:10.1371/ journal.pone.0007626 Funding: University of California Museum of Paleontology provided funding to MBG. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Received May 28, 2009; Accepted September 8, 2009; Published October 27, 2009 * E-mail: jhorner@montana.edu