# Pachycephalosaurus wyomingensis

> A dome-headed dinosaur from the latest Cretaceous of western North America, a neighbour of T. rex. Its skull roof was a thick dome of solid bone; injuries on many domes suggest that pachycephalosaurs butted heads.

- Classification: Dinosauria (clade) > Ornithischia (clade) > Pachycephalosauria (clade) > Pachycephalosauridae (family) > Pachycephalosaurus (genus) > Pachycephalosaurus wyomingensis (species)
- Length: 4.5 m
- Hip height: 1.2–1.6 m
- Mass: 370–450 kg
- Age: 72.1–66 million years ago (Late Cretaceous)
- Fossils found in: Hell Creek Formation (Montana); Lance Formation (Wyoming); United States
- Diet: herbivore
- Described: Charles W. Gilmore, 1931
- In films: The Lost World: Jurassic Park (1997)

Canonical page: https://dinodex.club/dinosaurs/pachycephalosaurus-wyomingensis
Last updated: 2026-09-27

## Overview

Pachycephalosaurus wyomingensis lived in western North America at the end of the Cretaceous, in the Hell Creek and Lance formations. Charles Gilmore named the species in 1931 as Troodon wyomingensis, from a skull dome found in Niobrara County, Wyoming; Barnum Brown and Erich Schlaikjer created the genus Pachycephalosaurus in 1943.

It is known mostly from skulls. The skull roof formed a high dome of dense bone, ringed with bony knobs and spikes. Jack Horner and Mark Goodwin (2009) argued that the flat-headed, spiky "Dracorex" and "Stygimoloch" are younger growth stages of Pachycephalosaurus, whose dome inflated and spikes shrank as it grew.

How the dome was used is debated. A survey of 109 pachycephalosaurid skulls found healed lesions on 22% of the domes, clustered at the top, which fits head-to-head butting (Peterson et al. 2013). Flat-headed individuals had no such injuries.

## Name meaning

"Thick-headed lizard", from Greek pachys ("thick"), kephalē ("head") and sauros ("lizard") (Brown & Schlaikjer 1943); wyomingensis for Wyoming (Gilmore 1931).

## Sources

1. (2026). Paleobiology Database: Pachycephalosaurus occurrences. The Paleobiology Database (paleobiodb.org), data service 1.2, accessed 2026-09-23. https://paleobiodb.org/data1.2/occs/list.txt?base_name=Pachycephalosaurus&show=coords,paleoloc,strat,loc,ref&pgm=gplates
2. (2026). Wikipedia: Pachycephalosaurus. Wikipedia (English), accessed 2026-09-23. https://en.wikipedia.org/wiki/Pachycephalosaurus
3. Brown, B. & Schlaikjer, E. M. (1943). A study of the troödont dinosaurs with the description of a new genus and four new species. Bulletin of the American Museum of Natural History 82(5): 115-150.
4. Cohen, K. M., Harper, D. A. T., Gibbard, P. L. & Car, N. (2023). International Chronostratigraphic Chart (v2023/09). International Commission on Stratigraphy. https://stratigraphy.org/ICSchart/ChronostratChart2023-09.pdf
5. Gilmore, C. W. (1931). A new species of troödont dinosaur from the Lance formation of Wyoming. Proceedings of the United States National Museum 79(9): 1-6. https://doi.org/10.5479/si.00963801.79-2875.1
6. Horner, J. R. & Goodwin, M. B. (2009). Extreme cranial ontogeny in the Upper Cretaceous dinosaur Pachycephalosaurus. PLoS ONE 4: e7626. https://doi.org/10.1371/journal.pone.0007626
7. Paul, G. S. (2016). The Princeton Field Guide to Dinosaurs (2nd edition). Princeton University Press.
8. Peterson, J. E., Dischler, C. & Longrich, N. R. (2013). Distributions of cranial pathologies provide evidence for head-butting in dome-headed dinosaurs (Pachycephalosauridae). PLoS ONE 8: e68620. https://doi.org/10.1371/journal.pone.0068620

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Cite as: "Pachycephalosaurus wyomingensis". DinoDex. https://dinodex.club/dinosaurs/pachycephalosaurus-wyomingensis (updated 2026-09-27).