The Ankylosaurus, recognized by its armored body and club-like tail, was a herbivorous dinosaur. Its name, meaning “bent lizard,” refers to the thick bony plates fused into its skin, offering substantial protection. These unique defensive adaptations make it a well-known ancient reptile.
Ankylosaurus’s Time on Earth
Ankylosaurus lived during the Late Cretaceous Period, from about 68 to 66 million years ago. This timeframe places its existence at the very end of the Mesozoic Era, often called the “Age of Dinosaurs.” It was among the last non-avian dinosaurs to roam Earth before the major extinction event that ended the Mesozoic.
Its fossils have been discovered across western North America, including Montana, Wyoming, and Alberta. Ankylosaurus belonged to a broader group of armored dinosaurs known as Ankylosauria. These creatures were characterized by their quadrupedal stance and extensive bony armor.
The World of the Late Cretaceous
During the Late Cretaceous, the global climate was considerably warmer than today, though a gradual cooling trend was evident towards the period’s end. There were no polar ice caps, and high sea levels created numerous shallow inland seas. The environment where Ankylosaurus lived, in western North America, featured warm temperatures and lush vegetation.
Plant life in the Late Cretaceous saw significant diversification, particularly with the rise of flowering plants, also known as angiosperms. While earlier plant forms like conifers, ferns, and cycads were still present, flowering plants became increasingly common. This rich flora provided a diverse food source for large herbivores like Ankylosaurus.
Ankylosaurus shared its habitat with a variety of other large dinosaurs, including formidable predators and other plant-eaters. Tyrannosaurus rex, a dominant carnivore, also roamed western North America during this period. Another prominent contemporary was Triceratops, a large, three-horned herbivore that lived from about 68 to 66 million years ago.
Unearthing Ancient Eras
Paleontologists determine the age of dinosaur fossils using scientific methods, as directly dating the fossilized bone is often challenging. One primary approach involves analyzing the rock layers where fossils are found, a technique known as stratigraphy. Sedimentary rocks, where most fossils are preserved, form in layers over millions of years, with older layers typically found beneath younger ones.
To establish more precise ages, scientists employ radiometric dating on volcanic rock layers located above or below the fossil-bearing sediments. These volcanic ash layers contain minerals with radioactive elements, such as uranium, that decay at a predictable and constant rate. By measuring the proportions of the original radioactive element and its stable decay products, scientists can accurately calculate the age of these igneous layers.
Uranium-lead dating is effective for materials millions of years old, making it suitable for dinosaur-era samples, unlike carbon-14 dating, which is only useful for much younger specimens. This “bracketing” of fossil-rich sedimentary layers between datable volcanic layers allows paleontologists to determine a time range for the fossils. Additionally, “index fossils”—remains of organisms known to have existed during a specific, well-defined geological period—can help correlate and date rock strata across different locations.