Paleontological Evidence Against a Major Geographic Barrier at about the Paleolatitude of Colorado, USA, during the Late Campanian (Late Cretaceous): The Conspicuous Absence of Endemic Subclades of Chasmosaurine Ceratopsid (Horned) Dinosaurs and Its Significance

Abstract

Several paleontologists have suggested that a major geographic barrier at about the paleolatitude of Colorado either prevented or severely restricted biogeographic exchange between the northern and southern regions of western North America during the Late Campanian. However, the origin and nature of this barrier remains enigmatic. In the present study, this hypothesis is tested by determining whether the diversification of Late Campanian chasmosaurine ceratopsid (horned) dinosaurs was affected by the presence of a barrier or, in other words, whether the biogeographic distribution of closely related species was nonrandom with respect to a line of paleolatitude drawn across Colorado. The results of this test indicate that there could not have been a major geographic barrier, which has implications for paleoclimatic and paleogeographic reconstructions of the Colorado region during its early Laramide history.