PALEOECOLOGY OF A MAASTRICHTIAN VERTEBRATE COMMUNITY FROM MONTANA

The Hell Creek Formation is one of the most productive dinosaur-bearing formations in the world, and continues to produce abundant remains of a wide diversity of Late Cretaceous vertebrates. Of particular note are the numerous microvertebrate-bearing sites of this region, which have been studied to examine faunal change across the K/T boundary. The Koenig Site, a new microvertebrate-bearing locality from the Lower Hell Creek Formation in Petroleum County, Montana, is described here and compared to well-known sites in eastern Montana, Wyoming and Canada. This site is of particular significance because the fossil bearing horizon occupies a relatively low stratigraphic position, close to the boundary with the underlying Fox Hills Formation, which represents a slightly earlier time interval than most known Hell Creek microvertebrate sites. Also, its location places it among the most western of these sites, geographically extending the existing sample of Lancian microvertebrate communities

Specimens were surface collected from a fossiliferous layer within a tan, well-sorted, fine-grained sandstone bed that was deposited about 160 km west of the continental seaway. Specimens were identified to the most precise taxonomic level possible (often this was family level or higher due to excessive water-wear) and were assigned to one of several diet and habitat categories, based on morphology, previous studies, and/or similar extant relatives.

At the Koenig site, diversity is highest among dinosaurs, followed by osteichthyans, then turtles. Specimen abundance is highest for osteichthyans, then dinosaurs and turtles. The fauna is dominated by terrestrial or amphibious taxa, consisting mostly of small carnivores. Although the site is both earlier and farther west than most Lancian-age sites, it shows broad similarities with them in taxonomic content and abundances. In general, the Koenig site produced more dinosaur specimens and significantly fewer amphibian and mammal specimens, but these differences are more likely taphonomic than environmental. The Koenig site fauna supports the interpretation that much of the Hell Creek depositional environment shared a similar vertebrate fauna throughout most of Lancian time, and suggests that little substantial change occurred prior to the end of the Cretaceous.