preserve distinct faunas. The upper portion of the formation is more diverse and preserves better quality fossils. However, many of the taxa that supposedly distinguished it as a separate fauna have since been found in older sediments. In particular, Gryposaurus latidens and Hypacrosaurus have been found to coexist with Maiasaura. Further, there are fossil teeth that seem to show the presence of certain taxa are unbroken throughout the whole formation. Nevertheless, some true changes in faunal composition seem to occur in the upper Two Medicine. The appearance of Maiasaura in the formation precedes the arrival of a diverse variety of other ornithischians. According to David Trexler, thorough examination of strata found along the Two Medicine River (which exposes the entire upper half of the Two Medicine Formation) indicates that the apparent diversification was a real event rather than a result of preservational biases. The timeline below follows the stratigraphic chart presented by Horner et al. 2001. Dinosaurs Some of the dinosaurs from the formation have been speculated to show signs of drought related death. Very few articulated dinosaurs have been found in the formation; most specimens are isolated, bone bed, poorly preserved or broken remains. Early studies assumed that the Two Medicine Formation would have the same dinosaurs as the Judith River Formation. It was only in 1978, that it was discovered that the formation had endemic dinosaurs. Even some genera regarded as wide-ranging predators exhibited a species difference between the Two Medicine and other formations. No ecological barriers have been postulated apart from upland/lowland habitat preference differences between the Two Medicine and Judith River Formation. There is no unequivocal evidence for intermingling between the wildlife of the Two Medicine and geographically adjacent contemporary formations. Dinosaur remains are more common in the upper part of the Two Medicine. Ankylosaurs Avialans Ceratopsians Non-avialan eumaniraptorans Ornithopods An unidentified lambeosaurine has been collected from the same stratigraphic placement, west of Bynum, and is in preparation at The Montana Dinosaur Center Oviraptorosaurs The first find of an oviraptorosaur in Montana was an articular region from the lower jaw of Caenagnathus sternbergi, from the Two Medicine Formation, according to a 2001 paper by David J. Varrichio. This species had previously only been known from the Canadian province of Alberta. Varrichio observes that during the late Campanian, Alberta and Montana had very similar theropods despite significant differences in the types of herbivorous dinosaur faunas. Tyrannosauroids Other