Pachycephalosaurus, recognized by its distinctive dome-shaped skull, is an intriguing ancient dinosaur. This unique cranial feature, which could be up to 10 inches thick, gives the dinosaur its name, meaning “thick-headed lizard”. While its exact purpose is debated, it likely played a role in social behaviors or defense. This bipedal herbivore was estimated to be around 15 feet long and weigh approximately 1,000 pounds.
Pinpointing Pachycephalosaurus’s Era
Pachycephalosaurus roamed the Earth during the Late Cretaceous period, specifically the Maastrichtian Age, from approximately 72.1 million to 66 million years ago. Its existence concluded just before the major extinction event that marked the end of the dinosaur age. Fossils have been predominantly discovered in western North America, including Montana, South Dakota, Wyoming, and Alberta. These fossils are found in geological formations such as the Lance and Hell Creek formations.
How Scientists Date Dinosaur Fossils
Paleontologists use several methods to determine the age of dinosaur fossils. One primary technique is stratigraphy, which involves studying rock layers where fossils are found. This method operates on the principle that lower rock layers are generally older than those above them. By identifying the rock layer, scientists can estimate a fossil’s relative age.
Another method is radiometric dating, which provides a more precise numerical age for rocks. While fossils lack radioactive elements for direct dating, this technique applies to volcanic ash or igneous rocks found near fossil-bearing layers. Radioactive elements within these materials decay at a known, constant rate, acting like natural clocks. By measuring the ratio of parent elements to their decay products, scientists calculate the age of surrounding rock layers, bracketing the fossil’s age.
The World of the Late Cretaceous
The Late Cretaceous period had a generally warmer global climate. North America was divided by a vast inland sea, creating distinct landmasses. The climate was predominantly subtropical, with warm, humid conditions supporting lush vegetation. Flowering plants, or angiosperms, became increasingly dominant and diverse, alongside conifers and other plant types.
This ancient landscape was home to many other dinosaur species that coexisted with Pachycephalosaurus. Large predatory dinosaurs like Tyrannosaurus rex and herbivores such as Triceratops and Ankylosaurus shared these habitats. Early mammals were also present, though generally small. This rich flora and diverse fauna defined the world where Pachycephalosaurus thrived before the major extinction event that concluded the Mesozoic Era.