Colorado, known for its deep geological history and rich paleontological record, has long embraced its prehistoric heritage. Many U.S. states officially recognize a symbol of their past by designating a state fossil or dinosaur. This practice highlights the unique ancient life preserved within a state’s borders. Colorado’s designation stands out due to the abundance of Jurassic-era finds, promoting scientific education and celebrating the state’s natural identity.
The Distinction Between State Fossil and State Dinosaur
The classification of Colorado’s official prehistoric symbol is often confusing due to a semantic difference in legislative action. While many ask for the state fossil, Colorado specifically designated the Stegosaurus as its official state dinosaur. A fossil is a broad term referring to any preserved remains or impression of a once-living thing. Conversely, a dinosaur represents a specific type of prehistoric reptile, making its designation more precise than the general term “fossil.”
The selection of the Stegosaurus occurred in 1982 following a legislative effort championed by a group of Colorado school children. Governor Richard Lamm signed an executive order declaring the Stegosaurus the state fossil, pending a formal statute. This action formally established a dinosaur as the state’s symbol, blurring the general “fossil” designation with the specific “dinosaur” category. This legislative push was a successful example of civic engagement, solidifying the armored giant’s place in the state’s identity.
Defining the Stegosaurus
The Stegosaurus is one of the most recognizable dinosaurs, known for its distinctive anatomy. This large, herbivorous creature lived during the Late Jurassic Period, approximately 150 million years ago, primarily in western North America. Paleontologist Othniel Charles Marsh named the genus, meaning “roofed lizard,” because he initially believed the large plates lay flat along the dinosaur’s back like shingles.
Its most defining features are the two alternating rows of large, bony plates, known as scutes, running vertically along its spine. These plates were embedded in the skin rather than attached directly to the skeleton, which is why they are often found separated in fossil discoveries. The function of these plates has been debated, with theories suggesting they served as a display for species recognition or courtship. Another theory is that the extensive surface area helped regulate the dinosaur’s body temperature through a system of blood vessels.
The other notable characteristic is the weapon at the end of its tail, a cluster of four to ten sharp spikes called the thagomizer. These spikes, which could grow up to three feet long, were likely used as a defense mechanism against large predatory dinosaurs, such as Allosaurus. The Stegosaurus was a sizable animal, reaching lengths of up to 30 feet and weighing between five and seven tons.
Despite its massive body, the Stegosaurus possessed a remarkably small head and an extremely low brain-to-body ratio. Its brain was only about the size of a plum, leading to early speculation that the dinosaur required a “second brain” in its hip region to manage its large body. As a herbivore with a short neck, the Stegosaurus primarily browsed on low-lying vegetation like ferns, mosses, and cycads.
Key Discovery Sites in Colorado
Colorado’s designation of the Stegosaurus is directly tied to the state’s geological significance for Jurassic-era discoveries. Much of the state sits atop the Morrison Formation, a vast stretch of Upper Jurassic sedimentary rock that is a fertile source of dinosaur fossils in North America. This formation, composed of mudstone, sandstone, and siltstone, represents the remnants of ancient rivers and floodplains.
The first Stegosaurus fossils were discovered in 1877 near the town of Morrison, Colorado, along the Dakota Hogback. This initial discovery by Arthur Lakes was quickly followed by intense excavation, coinciding with the fierce paleontological rivalry known as the “Bone Wars.” The competition between Othniel Charles Marsh and Edward Drinker Cope drove rapid and extensive fossil collecting throughout Colorado and Wyoming.
Another important site is the Garden Park Fossil Area, located near Cañon City in Fremont County. Quarries in this area yielded three of the most complete Stegosaurus skeletons ever found, solidifying Colorado’s claim to the dinosaur. The abundance of high-quality specimens from the Morrison Formation cemented the Stegosaurus as the state’s prehistoric symbol.