Triceratops, a horned dinosaur characterized by three facial horns and a large bony frill, roamed western North America during the Late Cretaceous period, approximately 68 to 66 million years ago. Its distinctive appearance makes it one of the most recognizable prehistoric animals. The discovery of its fossils provides insights into the ancient world it inhabited.
The Initial Discoveries
The first fossil evidence attributed to Triceratops was a pair of brow horns, uncovered by George Lyman Cannon near Denver, Colorado, in 1887. These remains were sent to paleontologist Othniel Charles Marsh, who mistakenly identified them as belonging to an extinct bison, naming it Bison alticornis. As more complete remains surfaced, Marsh recognized his error and, by the following year, established the genus Ceratops.
The holotype specimen of Triceratops was collected in 1888 from the Lance Formation in Wyoming by John Bell Hatcher. Marsh initially categorized this specimen under the Ceratops genus. Hatcher’s expeditions proved highly productive, recovering over thirty Triceratops skulls for Marsh by 1892, significantly contributing to the early understanding of this dinosaur.
Key North American Fossil Localities
Triceratops fossils have been found in several North American states and provinces, primarily within Late Cretaceous rock formations. The most abundant discoveries come from two major geological units: the Hell Creek Formation and the Lance Formation. These formations represent environments from the final stages of the Age of Dinosaurs.
The Hell Creek Formation extends across parts of Montana, North Dakota, South Dakota, and Wyoming. Triceratops is the most frequently found dinosaur in this formation, accounting for approximately 40% of the dinosaur fossils discovered there. Two recognized species, Triceratops horridus and Triceratops prorsus, show a stratigraphic separation; T. horridus is typically found in lower layers, while T. prorsus appears in the upper third of the formation. A particularly complete Triceratops fossil, nicknamed “Horridus,” was unearthed in Montana.
The Lance Formation, located predominantly in Wyoming, is another significant source of Triceratops fossils. More than half of the currently known Triceratops specimens were excavated from the Lance Creek fossil beds near Newcastle, Wyoming. This formation is comparable in age to the Hell Creek Formation, with fossils dating back approximately 65 to 67 million years ago. Beyond these sites, Triceratops remains have also been recovered from the Evanston Formation, Denver Formation, and Laramie Formation in Colorado, and the Scollard Formation in Alberta, Canada. The Scollard Formation, in particular, has yielded specimens of Triceratops prorsus in its lower sections.
Geological Clues from Fossil Sites
The locations where Triceratops fossils are found offer insights into the ancient environments these dinosaurs inhabited. Triceratops lived until the Cretaceous-Paleogene extinction event, approximately 66 million years ago. The geological formations preserving their remains provide evidence of the landscapes of that time.
The Hell Creek Formation largely consists of fluvial sandstones and mudstone deposits from ancient floodplains, alongside isolated lake deposits. This suggests a subtropical lowland floodplain environment. The Lance Formation is characterized by grayish sandy shales, light-colored sandstones, and thin coal layers, indicating a potentially more coastal setting. The Scollard Formation in Canada, composed of sandstone, siltstone, mudstone, and coal, formed from sediments carried by ancient rivers from the Canadian Rocky Mountains and deposited in river channels and wide floodplains.
These sedimentary environments, particularly the swampy lands bordering the Western Interior Seaway, facilitated the rapid burial and preservation of organic remains. This quick burial process, which cut off oxygen, was conducive to fossilization. The frequent discovery of Triceratops teeth in these formations also suggests their diet consisted of tough vegetation, which would have been abundant in such lush, low-lying habitats. The high number of complete Triceratops skulls found in these areas indicates their robust structure had a greater chance of preservation.