Stegosaurus, with its distinctive plates and spiked tail, remains one of the most recognizable dinosaurs to have roamed Earth. This herbivorous quadruped lived during the Late Jurassic period, approximately 155 to 145 million years ago. Its unique appearance has captivated the public imagination and spurred extensive scientific inquiry into its life and environments. To understand this ancient creature, it is helpful to explore the specific locations where its fossilized remains have been unearthed.
Geographic Distribution of Stegosaurus Fossils
The vast majority of Stegosaurus fossil discoveries have occurred in the western United States. These finds primarily come from states like Colorado, Wyoming, and Utah. The extensive fossil record in this region is largely due to specific geological conditions that favored preservation.
Beyond North America, fossil evidence suggests a broader, though less common, distribution. Fragmentary remains in Portugal hint at a connection between continents during the Late Jurassic. This limited presence outside North America suggests optimal conditions for Stegosaurus were predominantly found in the western United States.
Key Fossil Formations and Discovery Sites
The most significant source of Stegosaurus fossils is the Morrison Formation, a vast geological rock unit across the western United States. Dating from about 157 to 150 million years ago, this formation has yielded a rich diversity of Late Jurassic dinosaur fossils, including the first nearly complete Stegosaurus skeletons. It is composed of various sedimentary rocks like mudstone, sandstone, and siltstone, with many fossils found in green siltstone beds and lower sandstones.
Initial discoveries occurred during the “Bone Wars” of the late 19th century. In 1877, Arthur Lakes made a significant find near Morrison, Colorado, leading to Othniel Charles Marsh naming the genus Stegosaurus. Another site is Como Bluff in Wyoming, where Lakes and William Harlow Reed collected the type specimen of Stegosaurus ungulatus. Marshall Felch discovered the first nearly complete Stegosaurus skeleton in 1885 in Garden Park, Colorado, contributing significantly to understanding its anatomy. These sites within the Morrison Formation have provided insights into Stegosaurus.
Ancient Habitats of Stegosaurus
The environments where Stegosaurus lived were characterized by a seasonally wet climate. These ancient landscapes consisted of extensive floodplains traversed by numerous river channels, alongside ponds and lakes, some ephemeral. This setting provided water resources for a diverse ecosystem.
Vegetation during the Late Jurassic was dominated by non-flowering plants. Stegosaurus grazed on low-lying plants such as ferns, cycads, and conifers, abundant in its habitat. Forests grew along river corridors, providing denser vegetation within the more open, savanna-like floodplains. This combination of open areas and riparian forests likely offered a varied diet and suitable cover for large herbivores.