life, were lacking in their samples; and cardiac cellular structures were absent. There was one possible patch with animal cellular structures. The authors found their data supported identification as a concretion of sand from the burial environment, not the heart, with the possibility that isolated areas of tissues were preserved. The question of how this find reflects metabolic rate and dinosaur internal anatomy is moot, though, regardless of the object's identity. Both modern crocodilians and birds, the closest living relatives of non-avian dinosaurs, have four-chambered hearts (albeit modified in crocodilians), so non-avian dinosaurs probably had them as well; the structure is not necessarily tied to metabolic rate. Paleoecology Temporal and geographic range True Thescelosaurus remains are known definitely only from late Maastrichtian-age rocks, from Alberta (Scollard Formation) and Saskatchewan (Frenchman Formation), Canada, and Wyoming (Lance Formation), South Dakota (Hell Creek Formation), Montana (Hell Creek), and Colorado (Laramie Formation), USA. With the exception of birds, it was one of the last genera of dinosaurs, its remains being found as close as 3 meters to the boundary clay containing the iridium layer that closes the Cretaceous. The Laramie Formation is the oldest formation that Thescelosaurus is known from, and magnetostratigraphy suggests an age of 69-68 Ma for the Laramie Formation. There are reports of teeth from older, Campanian-age rocks, particularly from the Dinosaur Park Formation of Alberta, but these specimens are not from Thescelosaurus and are much more likely those of Orodromeus. More specimens are known than have been officially described for this genus, such as the Triebold specimen, which has been the source of several skeletal casts for museums. When Galton revisited Thescelosaurus and Bugenasaura in 1999, he described the dentary tooth UCMP 46911 from the Upper Jurassic of Weymouth, England as cf. Bugenasaura. If it is indeed a tooth from a thescelosaur-like animal, this would significantly extend the stratigraphic range of the group. Habitat Conflicting reports have been made as to its preferred habitat; two papers suggest it preferred channels to floodplains, but another suggests it preferred the opposite. The possible preference for channels is based on the relative abundance of thescelosaur fossils in sandstones, representing channel environments, in comparison to mudstones, representing floodplain environments. No bonebeds or accumulations of multiple individuals have yet been reported. Dale Russell, in a popular work, noted that Thescelosaurus was the most common small herbivore in the Hell Creek Formation of the Fort Peck