Pachycephalosauridae cast replicas

Taylor Made Fossils

Pachycephalosauria (pronounced _) Greek for "thick-headed lizards") is a clade of ornithischian dinosaurs. Well-known genera include Pachycephalosaurus, Stegoceras, Stygimoloch, and Dracorex. Most lived during the Late Cretaceous Period, in what is now North America and Asia. They were all bipedal, herbivorous/omnivorous animals with thick skulls. In some species the skull roof is domed and several inches thick; in others, it is flat or wedge-shaped. The dome may be surrounded by nodes (for instance, Pachycephalosaurus), spikes (Stygimoloch), or both (Dracorex).

Candidates for the earliest known pachycephalosaur include Ferganocephale adenticulatum from the Middle Jurassic Period of what is now Kyrgyzstan and Stenopelix valdensis from the Early Cretaceous Period of what is now Germany, although Sullivan doubted that either of these species is pachycephalosaurs.

The function of the thickened skull roof has been heavily debated. It has been frequently asserted that individuals may have rammed each other head-on, as do modern-day mountain goats and musk oxen. It is also suggested that pachycephalosaurs could make their head, neck, and body horizontally straight, in order to transmit stress during ramming. However, in no known dinosaur can the head, neck, and body be oriented in such a position. Instead, the cervical and anterior dorsal vertebrae of pachycephalosaurs show that the neck was carried in an "S"- or "U"-shaped curve. (Carpenter, Kenneth (1997). "Agonistic behavior in pachycephalosaurs (Ornithischia: Dinosauria): a new look at head-butting behavior" (pdf). Contributions to Geology 32 (1): 19–25.)

Also, the rounded shape of the skull would lessen the contacted surface area during head-butting, resulting in glancing blows. Other possibilities include flank-butting, defense against predators, or both. The relatively wide width of pachycephalosaurs (which would protect vital internal organs from harm during flank-butting) and the squamosal horns of the Stygimoloch (which would have been used to great effect during flank-butting) add credence to the former.

Cast replicas reproductions
Family Pachycephalosauridae:
Alaskacephale
Colepiocephale
Goyocephale
Hanssuesia
Homalocephale
Prenocephale (incl. Sphaerotholus)
Stegoceras (incl. Ornatotholus)
Tylocephale

Tribe Pachycephalosaurini
Dracorex - a possible juvenile form of Pachycephalosaurus
Pachycephalosaurus
Stygimoloch - a possible juvenile form of Pachycephalosaurus

Pachycephalosauridae incertae sedis (uncertain placement)
Wannanosaurus

Nomina dubia (doubtful names)
Gravitholus
Ferganocephale
Heishansaurus (probably an ankylosaur)
Micropachycephalosaurus
"Stegoceras" bexelli

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