Pachycephalosaur Dinosaur Fossil Vertebra

Description: The Pachycephalosauria, meaning thick headed lizards, is a family of dinoaurs from Order Ornithischia that includes such well known genera as Pachycephalosaurus, Stegoceras, Stygimoloch, and Dracorex. Most lived during the Late Cretaceous Period in what is now North America and Asia. They probably traveled in herds, were bipedal, and herbivorous/omnivorous animals charaterized by thick skulls. Some had a domed skull roof that was several inches thick and bearing nodes.

The function of the thickened skull roof has been heavily debated. It has been frequently postulated 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. The fossil record suggests that the earliest pachycephalosaurs arose in Asia about 85 million years ago, and were relatively small. Early genera ostensibly crossed the land bridge that during the Cretaceous times connected Asia and North America. North American genera evolved to be larger than those in Asia.