THE LATE PLEISTOCENE VERTEBRATE FAUNA FROM THE MERRELL LOCALITY, BEAVERHEAD COUNTY, MONTANA

In 1988, Lima, Montana resident Don Merrell discovered fossil bones on the southwest shore of Lima Reservoir. Merrell alerted the Bureau of Land Management (BLM) about the find. The BLM and University of Montana-Missoula collected fossils from the site during 1988 and 1989. This effort yielded 10 taxa (Dundas, 1990). Subsequent excavations at the site by the Museum of the Rockies in 1994, 1995, and 1996 resulted in a fossil collection that doubled the previously known fauna (Dundas, 2005).

The Merrell locality vertebrate fauna now includes 19 taxa: Osteichthyes (bony fishes), Anas cf. A. platyrhynchos (Mallard duck), Olar buccinator (Trumpeter swan), cf. Rana (true frogs), Lemmiscus curtatus (sagebrush vole), Ondatra zibethicus (muskrat), Spermophilus sp. (ground squirrel), Castor canadensis (beaver), Canis latrans (coyote), Canis lupus (gray wolf), Homotherium serum (Scimitar cat), Ursus sp. (bear), cf. Antilocapra americana (American pronghorn), Cervidae (genus indet., large species), cf. Odocoileus sp. (white-tail or mule deer), Bison sp. (bison), Camelops sp. (large camel), Equus sp. (horse), Mammuthus columbi (Columbian mammoth).

While much of the fauna still lives in the area, several taxa are extinct, including Homotherium serum, Camelops, Equus and Mammuthus columbi. The presence of Homotherium serum and Olar buccinator are of particular interest due to their rarity in the fossil record in North America.

All taxa at the site represent a minimum of one individual, except Bison, Equus and Mammuthus columbi. At least two Bison are present; a juvenile and an adult. A juvenile and adult Equus are also present, although it is likely that more individuals are represented based on stratigraphic location of the juvenile remains. At least three mammoths, two adults and one subadult (or juvenile), occur at Merrell.

The Merrell fauna is not all the same age. Five stratigraphic units occur at the site, two of which produce most fossils. However, it is not possible to refer all fossils at the site to faunules due to extensive bioturbation and because some specimens were recovered from the reservoir shore and thus lack stratigraphic context. The two primary fossil bearing units, Stratum D, a debris flow on the north end of the site, dates to ca. 28,000 and 22,000 B.P. and Stratum B (and upper Stratum A) dates to ca. 40,000 B.P.