CURRENT RESEARCH IN THE PLEISTOCENE Vol. 23, 2006 PROOF COPY 185 Taphonomic Processes Associated with the Merrell Local Fauna (Pleistocene, Rancholabrean) in the Greater Yellowstone Ecosystem, Centennial Valley, Southwestern Montana Christopher L. Hill The Merrell Local Fauna (MLF), recovered from sedimentary deposits near the Red Rock River within Centennial Valley in southwestern Montana, com- prises four classes of taxa: Osteichthyes (bony fish), Aves (waterfowl), Am- phibia (amphibians), and Mammalia (Dundas et al. 1996; Hill and Davis 2005; Hill 2006). The locality demonstrates the diversity of the Rancholabrean fauna within the Greater Yellowstone Ecosystem. Finite radiocarbon ages obtained from 13 direct radiocarbon measurements made on bone range from 49,350 ± 1500 RCYBP (Beta-116519) to 19,310 ± 90 RCYBP (Beta-77826). Several measurements indicate some remains are > 52,800 RCYBP (see below). The faunal assemblages that form the MLF have been affected by a variety of taphonomic processes resulting from pre-burial deposition, burial, and post- burial events. Stratigraphic contexts and sedimentologic facies associated with the MLF reflect variability in depositional and post-depositional processes, providing information on the factors leading to the accumulation of the fossils. Five strata have been recognized (Figure 1). Vertebrate remains found within stratum A are usually rare and isolated, except near its contact with stratum B. An example of an isolated find within stratum A is a patella of a proboscidean (cf. Mammuthus). It is likely that some of the fossils found within stratum A, especially near its upper contact with stratum B, have been moved by post- depositional events. The first taphonomic context in which there are higher frequencies of vertebrate bones is along the interface of strata A–B and in the lowest part of stratum B. There are no articulated specimens, but there are concentrations of bones, tusk, and teeth of mammoth. Other faunal materials from this taphonomic context include Ondatra zibethecus (muskrat) and bivalves. These may include bones that first accumulated on the surface of stratum A then were buried within stratum B, as well as elements that accumulated during the deposition of stratum B. Radiocarbon measurements, if reliable, suggest that this taphonomic context contains a temporally mixed assemblage. Fragments of mammoth teeth were dated at > 52,800 RCYBP (SR-6012, SR-6013), while 14 C ages on tusk fragments are 32,470 ± 270 RCYBP (Beta-111325) and 23,120 ± 1190 RCYBP (SR-6014). These could reflect a taphonomic context associated with surface exposure within a small basin and burial in or incorpo- ration into a marsh. Christopher L. Hill, Department of Anthropology, Boise State University, Boise, ID; e-mail: chill2@boisestate.edu 1 2 3 4 5 5