Systematic position of Litomylus(?) alphamon Van Valen (Mammalia: Insectivora): further evidence for the Late Paleocene age of Swan Hills Site-1 in the Paskapoo Formation of Alberta

Abstract

The Swan Hills are erosional remnants of a once-continuous plateau lying between the Athabaska River and Lesser Slave Lake in the north-central part of Alberta, western Canada. Fossils were first discovered in the Paskapoo Formation here in 1964 by L. S. Russell, who described a small mammalian fauna from Swan Hills Site-1 (Russell, 1967). Russell's collection from Site-1 was interpreted (correctly) as representing the Tiffanian Land-Mammal Age (Late Paleocene). Of particular interest, Russell (1967) described a new primate species of the plesiadapiform family Carpolestidae, “Carpolestes” cygneus, based on fragmentary remains from Site-1. This species was later transferred to Carpodaptes by Rose (1975). Judging from the evolutionary grade of Carpodaptes cygneus, Rose (1977) regarded Swan Hills Site-1 as early or early middle Tiffanian in age. Additional work on C. cygneus at other Canadian sites indicated that Site-1 might be early late Tiffanian in age (Krause, 1978). This distinction is important because Carpodaptes has a more detailed evolutionary record in Wyoming and Montana, and correct attribution of the name C. cygneus, originally based on three isolated teeth, to samples better known elsewhere necessarily requires precise correlation. The holotype and type sample of C. cygneus, by themselves, are too fragmentary and limited to characterize the species. Species of Carpodaptes are among the most common and useful fossils available for precise dating of sediments associated with Laramide tectonic deformation in the Western Interior. At 55° north latitude, Swan Hills Site-1 remains the most northerly locality in North America yielding Paleocene mammals.