INTRODUCTION Romer (1966) proposed a new suborder, “Proteutheria,” for insectivorous mammals that had no clear relationship to living insectivorans. Romer's concept of “Proteutheria” included leptictids, zalambdalestids, anagalids, paroxyclaenids, pantolestids, ptolemaiids, tupaiids, pentacodontids, apatemyids, and macroscelidians. “Proteutheria” as constituted by Romer is an unnatural grouping and cannot be sustained phylogenetically. According to McKenna and Bell (1997), the lowest-level grouping that contains all of the mammals discussed in this chapter is the Magnorder Epitheria (cohort Placentalia). Within the Epitheria, Romer's “proteutherians” are distributed unevenly in the Superorders Leptictida (leptictids) and Preptotheria. “Proteutheria” is perhaps still best thought of as a paraphyletic group of archaic insectivorous mammals traditionally not placed in Lipotyphla. Bloch, Rose, and Gingerich (1998) showed that taxa included in this group generally exhibit larger body size than those grouped in Lipotyphla and argued that the term was still useful in representing an ecologically coherent subset of Paleogene faunas. We include Palaeoryctidae, Cimolestidae, Pantolestidae, and Apatemyidae as members of this informal group. Palaeoryctidae are known from the early Paleocene through early Eocene in North America. Some species from the Late Cretaceous of Asia and Europe, and from the late Paleocene to early Eocene of Africa, may also be palaeoryctids (McKenna and Bell, 1997). Cimolestids first appear in the Late Cretaceous in North America, represented by Cimolestes, and survive through the Duchesnean, last represented by Didelphodus.