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Roger Weller, geology instructor

by Matt Crabb
Historical Geology
Spring 2010


                                                 The Pachycephalosaurus


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          The Cretaceous period was best known as the “Age of the Dinosaur.”  It was a time where many dinosaurs roamed the earth, including the Tyrannosaurus Rex, the Triceratops, and of course, the Pachycephalosaurus.  The Pachycephalosaur were a fairly small family of dinosaur best known for their heavy skullcaps as big as their name, going from mildly thick to the truly dense.  The Dome-headed reptile came from the suborder Pachycephalosauria (thick skulled herbivores) and the order Ornithischia (bird-hipped).  They could stand to be up to fifteen feet tall (the length of a large car) and weighed around 950 pounds.  They were also known to have a distinct sense of smell with spiky knobs on their snouts and the back of their heads.  This bipedal creature walked on two powerful hind legs and had 3-toed feet, short, clawed 5-fingered hands, and a stiff tail of interwoven tendons.  They were also fairly slow and were said to run with their backs level to the ground, usually walking on all fours when it came to eating.  Among this creature’s advantages was the binocular vision given by its large round eyes.  Their trademark skull could grow to up to 10 inches thick. The later Pachycephalosaurs contained a foot of solid bone structure on the roof of their skulls, which didn’t leave much room for brain matter.  These creatures lived during the late Cretaceous period towards the end of the Mesozoic Era.

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          With this dinosaur being the equivalent of a linebacker in a football game, one might wonder how the Pachycephalosaurus defended itself in its environment.  It was suspected at one time that this creature was a bipedal equivalent to that of a bighorn sheep or a musk oxen.  For a long time it was a misconception that this reptile used its massive skullcap for head-on ramming against its enemies for dominance, mating rights, and self defense against predators.  In order to do so it was also believed that the Pachycephalosaurus would straighten its whole body horizontally for momentum, which was proven false due to its U or S-shaped structure. A paleontologist by the name of Mark Goodwin specialized in the analysis of Pachysephalosaur skulls and brought an end to that myth.  Finding no scars or long-term damage on these skulls and discovering the skulls were actually susceptible to damage, it was proposed instead that these creatures engaged in what is called flank-butting.  By ramming the sides of other animals, the Pachycephalosaurus would deal more damage and remain amongst the living, which would be a different story with a head-on ram.  This engagement of course would only happen if the act of intimidation failed. 


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        As for their habitat, the Pachysephalosaurus roamed the land of Laurasia, (the landmass connecting North America and Asia). Though the Pachycephalosaurs are said to be herbivores and omnivores, it is still unknown exactly what it was they lived off of.  Their small-ridged teeth would hinder them from eating the tougher plants thus it is assumed their basis for diet consisted of fruit, insects, and leaves.  They also used their teeth for shredding plants, making them easier to eat.

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          There has been somewhat of a deficit of information uncovered about this dinosaur since the only part of the anatomy that became fossilized was usually the skull.  A fossil collector named Ferdinand Vandiveer Hayden had first found remains of this creature in 1859.  Hayden discovered the bone fragment at the end of the Missouri River (presently known as the Lance Formation), and described it to be armor possibly from an armadillo-like creature.  Charles W. Gilmore gave the type P. wyomingensis for the Pachycephalosaur species in 1931.  He placed the species with the Troodon as the type T wyomengensis, based on teeth characteristics.  In 1943 Barnum Brown and Erich Maren Schaiker discovered a skull almost in its entirety, thus confirming the genus Pachycephalosaurus, with the species type T wyomengensis. 


          The end of the Cretaceous period (65 million years ago) came with the second most massive extinction in the earth’s history.  There have been many speculations on what caused the End-Cretaceous extinction such as meteorite impacts, volcanic eruptions.  Another speculation would be the K-T boundary that contained evidence found in a layer of sediment deposition containing Iridum, which is normally located within the earth’s mantle and meteors.  This mass extinction marked the end of nearly all life.