Pachycephalosaurus

Pachycephalosaurus
Temporal range: Late Cretaceous (Maastrichtian), 70–66 Ma
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Cast of the "Sandy" specimen, Royal Ontario Museum
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: †Ornithischia
Clade: †Neornithischia
Clade: †Pachycephalosauria
Family: †Pachycephalosauridae
Tribe: †Pachycephalosaurini
Genus: †Pachycephalosaurus
Brown & Schlaikjer, 1943
Type species
†Pachycephalosaurus grangeri
Brown & Schlaikjer, 1943
(Junior synonym of P. wyomingensis)
Species
  • †P. wyomingensis
    (Gilmore, 1931) (conserved name)
  • †P. spinifer?
    (Galton & Sues, 1983)
Synonyms
Synonyms of P. wyomingensis
  • Tylosteus ornatus
    Leidy, 1872 (rejected name)
  • Troodon wyomingensis
    Gilmore, 1931
  • Pachycephalosaurus grangeri
    Brown & Schlaikjer, 1943
  • Pachycephalosaurus reinheimeri
    Brown & Schlaikjer, 1943
  • Stenotholus kohleri
    Giffin, Gabriel & Johnson, 1988[1]
  • Stygimoloch spinifer?
    Galton & Sues, 1983
  • Dracorex hogwartsia?
    Bakker et al., 2006

Pachycephalosaurus (/ˌpækɪˌsɛfələˈsɔːrəs/;[2] meaning "thick-headed lizard", from Greek pachys-/παχύς- "thickness", kephalon/κεφαλή "head" and sauros/σαῦρος "lizard")[3] is a genus of pachycephalosaurid ornithischian dinosaur. The type species, P. wyomingensis, is the only known species, but some researchers argue that Stygimoloch might be a second species, P. spinifer, or a juvenile specimen of P. wyomingensis. It lived during the Maastrichtian age of the Late Cretaceous period in what is now western North America. Remains have been excavated in Montana, South Dakota, Wyoming, and Alberta. The species is known mainly from a single skull, plus a few extremely thick skull roofs (at 22 cm or 9 in thick). More complete fossils would come to be found in the following years.

Pachycephalosaurus was among the last species of non-avian dinosaurs on Earth before the Cretaceous–Paleogene extinction event. The genus Tylosteus has been synonymized with Pachycephalosaurus, as have the genera Stygimoloch and Dracorex, in recent studies.[4][5]

Like other pachycephalosaurids, Pachycephalosaurus was a bipedal herbivore, possessing long, strong legs and somewhat small arms with five-fingered hands. Pachycephalosaurus is the largest-known pachycephalosaur, known for having an extremely thick, slightly domed skull roof; visually, the structure of the skull suggests a ‘battering ram' function in life, evolved for use as a defensive mechanism or intra-species combat, similar to what is seen with today's bighorn sheep or muskoxen (with male animals routinely charging and head-butting each other for dominance). This hypothesis has actually been highly disputed in recent years.

  1. ^ Giffin, Emily B.; Gabriel, Diane L.; Johnson, Rolf E. (January 22, 1988). "A New Pachycephalosaurid Hell Creek Formation of Montana". Journal of Vertebrate Paleontology. 7 (4). Taylor & Francis, Ltd.: 398–407. doi:10.1080/02724634.1988.10011672. JSTOR 4523163. Retrieved November 13, 2020.
  2. ^ "Definition of pachycephalosaurus | Dictionary.com". www.dictionary.com. Retrieved February 22, 2020.
  3. ^ Colbert, Edwin H. (Edwin Harris); Knight, Charles Robert (1951). The dinosaur book: the ruling reptiles and their relatives. New York: McGraw-Hill. p. 152.
  4. ^ Cite error: The named reference HG09 was invoked but never defined (see the help page).
  5. ^ Goodwin, Mark B.; Evans, David C. (2016). "The early expression of squamosal horns and parietal ornamentation confirmed by new end-stage juvenile Pachycephalosaurus fossils from the Upper Cretaceous Hell Creek Formation, Montana". Journal of Vertebrate Paleontology. 36 (2): e1078343. Bibcode:2016JVPal..36E8343G. doi:10.1080/02724634.2016.1078343. ISSN 0272-4634. S2CID 131282984.