Fossil evidence indicates that the common late Maastrichtian species Triceratops horridus (Marsh, 1889) had a geographic range spanning from Colorado in the south to Saskatchewan in the north. Centered within the heart of this geographic range, our field work in the Upper Hell Creek Formation of eastern Montana has produced a total of thirty-six individual Triceratops localities, with a stratigraphic range spanning some 60 m. We made the observation that all thirty-six individual Triceratops specimens were preserved in bentonite-rich, fine-grained fluvio-lacustrine mud and siltstones, with ferruginous staining and gypsum deposits occurring along the natural joints of the rock matrix. Although other specimens of this genus have been reported to occur within sandstone deposits in the Hell Creek Formation (Hatcher, 1907), other authors have more recently described specimens which were preserved in mud and siltstones (Goodwin et al., 2006; Hatcher, 2006). This is of particular interest for its implications for Triceratops paleobiology. With Triceratops being the most commonly occurring dinosaur throughout the deposition of the Hell Creek sediments, such a strict preservational matrix for Triceratops could suggest that this was not a herding animal.

This specific preservational matrix for Triceratops is indicative of a habitat of shallow freshwater lowland environments, supported further by the presence of the paleobotanical fossils found in each quarry. This field data, in addition to the lack of ceratopsian bonebeds throughout the Hell Creek Formation, leads to the conclusion that Triceratops lived as solitary individuals or in small family groups, as opposed to living in vast herds, in habitat near the flood plains that would favor their preservation, and account for their regional dominance of the Hell Creek dinosaurian fossil record.