Stygimoloch

Stygimoloch is a pachycephalosaurid dinosaur from the Late Cretaceous of North America.

Characteristics
Styigimoloch are thick-skulled herbivores, covered in light-red scales and darker osteoderms and spikes running down their backs and on their heads. A dome covers the top of their heads, used in both defense and ruts during the mating season. Stygimoloch have few defenses against anything larger than a Deinonychus, and as such prefer to run away from such predators in most cases. In spite of their cowardly attitude towards predators, Stygimoloch are very territorial towards most herbivores that aren't large enough to keep them at bay or able to fight larger predators, chasing them away from their grazing areas. A Stygimoloch's diet is very diverse, and allows them to mow down vast amounts of vegetation while foraging. As such, they are incredibly ecologically destructive when introduced to habitats where they don't belong.

During the mating season, Stygimoloch will begin head-butting and flank-butting matches in order to establish a hierarchy of which males of the herd will mate with the females. When a male wins one of these conflicts, he will mark this with the release of urine. Stygimoloch breed at a substantial rate, tend to be higher than most of the predators native to these habitats and Deinonychus alone can control.

Arrival of Vulture Squad
Stygimoloch were among the species brought to Vulture Valley in Vietnam by the failure the first USSR particle collider. Herds of the pachycephalosaurs would migrate out of the valley and begin setting up populations in much of Vietnam. Months after their arrival, Andrei Wynn was rammed by a male, nearly breaking his legs.

A year later when Vulture Squad was called to the valley to investigate the disappearance of a platoon of Green Beret, half of the squad encountered a herd of Stygimoloch doing their mating rut in an orchard, and Gerald Keyes recognized the animals from one of Leon's books. The group attempted to sneak past the herd, but a male accidentally urinated on Eli Taylor's face. Eli attempted to shoot the animal, but was calmed down by Xavier Wise when a pack of Deinonychus attacked the herd, killing multiple Stygimoloch before attempting to herd them into more kill positions. Once the herd began stampeding, Vulture Squad attempted to run with them in order to be less likely targets of the predators, but the herbivores constantly butted them for space. Eventually, this knocked Eli over, trampling him until Charlie Miller broke out and shot into the air to scare the dinosaurs away from his friend. The herd would continue running away from the Deinonychus as the pack shifted their attention to Vulture Squad.

Destruction of the Collider
Once Vulture Squad had regrouped and been joined by General Amadeus Jericho's Black Ops and Andrei, the groups encountered a mixed herd of Stygimoloch, Triceratops, and Hypsilophodonts. The soldiers would warily keep their guns pointed at the herd until a feeding frenzy of Kaprosuchus attacked, scaring off the herbivores.

Trivia

 * While Stygimoloch is counted as a separate genus in the Primitive War franchise, there is an ongoing debate on whether it was its own genus, a juvenile of the larger Pachycephalosaurus, or a species within that genus, with most evidence pointing towards juvenile.