RANGE EXTENSION OF SOUTHERN CHASMOSAURINE CERATOPSIAN DINOSAURS INTO NORTHWESTERN COLORADO

Abstract

T he Williams Fork Formation preserves a diverse dinosaur fauna containing at least nine saurischian and five ornithischian species. Among the dinosaur specimens recovered is a partial ceratopsian skull (SDMNH 43470) referable to the ceratopsid subfamily Chasmosaurinae (Diem, 1999). Chasmosaurines, or long-frilled ceratopsians, existed throughout western North America during the Campanian and Maastrichtian (Judithian, Edmontonian, and Lancian). Recent discoveries have renewed debate over the phylogenetic relationships and biogeographic history among the chasmosaurines (Forster et al., 1993; Lehman, 1996; Holmes et al., 2001). There are some latitudinal differences in occurrences of taxa. Northern chasmosaurines include Anchiceratops ornatus (Brown, 1914), Chasmosaurus belli (Lambe, 1902), C. irvinensis (Holmes et al., 2001), and C. russelli (Sternberg, 1940) from the upper Campanian Dinosaur Park Formation of Alberta, Canada (Dodson and Currie, 1990; Godfrey and Holmes, 1995; Holmes et al., 2001; Ryan and Russell, 2001). A. ornatus has also been reported from the upper Campanian to Maastrichtian Horseshoe Canyon Formation of Alberta, Canada (Eberth, 1997), as has Arrhinoceratops brachyops (Parks, 1925; Dodson and Currie, 1990). The common late Maastrichtian species Triceratops horridus (Marsh, 1889) ranges from Colorado in the south to Alberta and Saskatchewan in the north, while the less common Torosaurus latus (Marsh, 1891) has a slightly smaller, but similar range (Dodson and Currie, 1990), both occurring in the Lance and Hell Creek Formations or their equivalents. In the southern area, another Maastrichtian species of Torosaurus (Marsh, 1891), T. utahensis (Gilmore, 1946) from the North Horn Formation of Utah, Kirtland Shale in northwestern New Mexico, and the Javelina Formation of southwestern Texas, is sometimes recognized (Lehman, 1996). Some authors treat Torosaurus utahensis as a synonym of T. latus (Dodson and Currie, 1990). If this synonymy is correct, T. latus maintained a geographic range from Saskatchewan, Canada, in the …