Description and Classification

Pachysaurus was a bipedal herbivore, meaning it walked on two legs and ate plants. Like other members of the Pachycephalosauridae family, its most striking characteristic was the solid, dome-shaped skull, which could be several inches thick. Scientists believe this dome was made of dense bone. Pachysaurus is estimated to have been a medium-sized pachycephalosaur, likely reaching lengths of around 10 to 13 feet (3 to 4 meters) and weighing several hundred pounds. It would have had a relatively short, thick neck to support its heavy head, a bulky body, and a long, stiff tail that provided balance as it moved.

The classification of Pachysaurus places it within the group Pachycephalosauria, and more specifically, within the family Pachycephalosauridae. This family includes other well-known “bone-headed” dinosaurs such as Pachycephalosaurus and Stegoceras. While sharing many common traits with its relatives, ongoing studies aim to clarify its precise relationship to other genera within the family.

Distinguishing Features

Pachysaurus can be distinguished from other pachycephalosaurs by a combination of characteristics:

• The dome on its skull, while thick, was proportionally wider and slightly flatter on top compared to the more rounded domes of dinosaurs like Prenocephale.
• It possessed a unique pattern of bony knobs (osteoderms) around the rear and sides of the dome, which were more prominent and less densely packed than those seen in some other species.
• The bone texture on the surface of the dome suggests a well-developed covering of keratin, similar to the horns of modern animals, which might have added to its strength or appearance.
• Analysis of its vertebrae indicates a particularly robust neck structure, even for a pachycephalosaur, possibly hinting at more intense or frequent head-pushing or head-butting behaviors.

Paleoenvironment and Diet

Pachysaurus lived in what is now western North America during a time when the landscape featured warm, humid coastal plains, river systems, and forests. This environment supported a diverse range of plant life, which formed the diet of Pachysaurus. It likely browsed on low-growing vegetation, such as ferns, cycads, and flowering plants, using its relatively small, leaf-shaped teeth to shred plant material. It shared its habitat with many other famous dinosaurs, including hadrosaurs like Maiasaura, ceratopsians such as Styracosaurus, and predatory theropods like Gorgosaurus, a relative of Tyrannosaurus rex.

Significance and Ongoing Research

The study of Pachysaurus contributes to our understanding of the diversity and evolution of pachycephalosaurid dinosaurs. Like other pachycephalosaurs, the function of its thick skull dome is a topic of much discussion. Theories range from defense against predators, to display for attracting mates, to combat with rivals (flank-butting or head-pushing). The specific structure of the Pachysaurus dome provides more data points for these hypotheses.

Ongoing research on Pachysaurus focuses on finding more complete fossil specimens, which would help to refine its anatomical description and better understand its locomotion and overall biology. Comparative studies with other pachycephalosaur domes, including internal bone structure analysis using CT scans, aim to shed more light on how these domes grew and what stresses they could withstand. These findings help scientists piece together the behavior and social structures of these fascinating “thick-headed lizards” from the Late Cretaceous world.