Pachycephalosaurus wyomingensis
The pachycephalosaurs were bipedal, herbivorous
dinosaurs with distinctively thick-boned skull caps. They are often
referred to as the bone-headed dinosaurs (or dome-headed dinosaurs, or
thick-headed dinosaurs). The largest species and namesake of the group is
Pachycephalosaurus wyomingensis Gilmore, 1931, a famous component of
Montana’s Hell Creek Formation (Maastrichtian Stage, upper Upper Cretaceous,
~65-70 m.y.). Not surprisingly, the thick bony skull caps are the most
commonly found remains of this species (& of all pachycephalosaurs).
The snout and back of skull were covered in knobby spikes.
Pachycephalosaurs are usually inferred to have engaged
in head-butting (as do modern bighorn sheep), with the thickened skull caps
functioning as stress cushions to avoid brain damage. Some workers
suggest that head-to-flank pushing behavior was more likely in many
species. In Pachycephalosaurus wyomingensis, the bone layer above
the brain cavity got to be nine inches thick, plus skull caps are known with
scars. It’s safe to conclude that this particular species did engage in
head-butting.
Classification: Animalia, Vertebrata, Dinosauria, Ornithischia,
Genasauria, Cerapoda, Marginocephalia, Pachycephalosauridae
Pachycephalosaurus wyomingensis Gilmore, 1931 skeleton & skull (reconstructed;
above & below) from the near-uppermost Upper Cretaceous of Montana, USA.
(public display, Carnegie Museum of Natural History,
Pittsburgh, Pennsylvania, USA)
Mostly synthesized from Maryanska (1990), Forster
& Sereno (1997), Sues (1997), and Horner (2001).
References Cited:
Maryanska, T. 1990
Pachycephalosauria. pp. 564-577 in The Dinosauria.
Berkeley. University of California Press.
Forster, C.A. & P.C. Sereno. 1997.
Marginocephalians. pp. 317-329 in The Complete Dinosaur.
Bloomington, Indiana. Indiana University Press.
Sues, H.-D. 1997.
Pachycephalosauria. pp. 511-513 in Encyclopedia of
Dinosaurs. San Diego. Academic Press.
Horner, J. 2001. Dinosaurs Under the
Big Sky. Missoula, Montana. Mountain Press Publishing
Company. 195 pp.