INTRODUCTION

Fossil localities in the Garbani Channel deposits and other units of the Tullock Formation, Garfield and McCone Counties, northeastern Montana, have yielded large samples of latest Cretaceous (Lancian) and early Paleocene (Puercan and Torrejonian) vertebrates (Clemens 2002). Archibald (1982), Lofgren (1995), and Wilson (2004, 2005) have analyzed the Lancian and earliest Puercan (Pu1 interval zone) mammalian faunas of the area. Torrejonian local faunas have been analyzed by Clemens and Wilson (2009). In contrast samples of Pu2/Pu3 (undifferentiated) Puercan local faunas have yet to receive comparable attention. The primary goal of this paper is to help fill this gap through description and analysis of new material from the Pu2/Pu3 deposits in the Tullock Formation representing two species of Eoconodon ("Triisodontidae," Mammalia).

Comparisons are made with species of Eoconodon from other areas of the Western Interior, particularly the San Juan Basin, New Mexico (Williamson 1996, Clemens and Williamson 2005). The paleobiogeographic distribution of currently documented occurrences of these species provides support for the hypotheses that immigration played a significant role in the evolution of Puercan faunas after the extinctions marking the Cretaceous-Tertiary boundary and Puercan mammalian faunas of the Western Interior were characterized by distinct paleobiogeographic provincialism.