Role in the Series
Boneheads appear to be one of the more uncivilized races of the world depicted in the series, with three seen in The Land Before Time attacking Cera in a cave near the Mountains that Burn after Ducky, Petrie and Spike, who she had led into the hazardous area, are left behind without her noticing. They are scared off when a terrifying monster appears; however, the abomination is then revealed to be Littlefoot and the others (who he had rescued) covered in tar and using bones and branches. In The Land Before Time IV: Journey through the Mists, two battling pachycephalosaurs attempt to attack Littlefoot and his and friends in the Land of Mists.
However, peaceful Pachycephalosaurus living in harmony with other residents of the Great Valley are seen in in The Land Before Time V: The Mysterious Island, The Land Before Time XI: Invasion of the Tinysauruses and The Land Before Time XII: The Great Day of the Flyers, and even as hatchlings in the latter, as in The Land Before Time VI: The Secret of Saurus Rock.
Many theories have been put forward to these contrasting roles. Some scientists think pachycephalosaurs were omnivores and this existing in The Land Before Time may allow them to live in otherwise inhospitable places such as the Mountains That Burn and the Land of Mists; therefore the Boneheads that attacked Cera may have been trying to eat her. A deleted scene in The Land Before Time shows a group of "Crown-heads" who are dying of thirst guarding a copse of trees at an oasis from a herd of Gray-noses (Swimmers/Bigmouths) who are dying of starvation and guarding a pond from them. The two species will not share with each other simply due to segregation despite the fact that they will both die in the end. This extreme racism may account for attacking Cera. Also, as pachycephalosaurs are thought to have been territorial animals, territory matters may account for violence in both films.
Finally, it may be simply that the dinosaurs' surroundings influenced their behavior. The dinosaurs in the Great Valley live in a predator-free environment teeming with food and water, where multiple species live together in harmony, so they are more peaceful. The ones living in the caves near the Mountains That Burn, however, dwell in a harsh location where food is scarce and volcanic eruptions occur regularly, as well as struggling to survive constant menace from predators. As a result, they are more aggressive.
Pachycephalosaurus have been referred to by many different names in the Land Before Time series. The Pachycephalosaurus that attack Cera in The Land Before Time are called lizard-heads in the books "Friends in Need" and "The Land Before Time: The Illustrated Story", while the ones in a scene removed from the final film are called crown-heads both in the aforementioned books and in the May 1987 revision of the original film's script. In the credits for The Land Before Time XI: Invasion of the Tinysauruses, a Pachycephalosaurus is called a Bonehead.
- Some fans use the term "Domehead", which is used in reference to Stegoceras in "The Cave of Many Voices", to describe Pachycephalosaurus.