106 D. E. SAVAGE 



sortment of jaws and teeth and is one of the best of the Mesozoic 

 mammalian assemblages (Simpson, 1929). The early Cretaceous 

 record, at the threshold of dichotomy between eutherian (placental) 

 and metatherian (marsupial) mammals, is limited to a few tantaliz- 

 ing scraps of bone, isolated teeth and jaw fragments from a site 

 in north Texas (Patterson, 1956). The later Cretaceous land mammal 

 localities — principally in Wyoming, Montana, and Alberta — indi- 

 cate at present a curiously undiversified aggregate of multituber- 

 culates, didelphoids, and generalized eutherians. 



The Cenozoic mammals of North America inherited an array of 

 nonmarine environments that extended across the entire continent ; 

 for our emergent land mass has suffered only marginal inundation 

 through the last 70 million years. In the freshwater deposits of the 

 middle and southern latitudes, mammalian aggregates have been 

 uncovered that are delightfully complete and varied when compared 

 with earlier records, but they are woefully small as compared with 

 the obtainable living sample of the same area. With the exception 

 of the interesting Miocene and Pliocene faunas in Florida, the 

 fossil mammal sample of western North America must represent all 

 the Nearctic region. Very few pre-Pleistocene fossil mammal speci- 

 mens have yet been found east of the Mississippi River. 



Paleocene forms, tokened by skulls, dentitions, and some com- 

 plete skeletons, have been collected in the present Rocky Mountain 

 province. A few materials have been discovered in California 

 (McKenna, 1955), and one jaw came from a deep well in Louisiana 

 (Simpson, 1932). The better and more varied Paleocene assemblages 

 are in New Mexico, Utah, Wyoming, and Montana. 



Eocene mammalian local faunas extend from the West Coast into 

 the Rocky Mountain area and from British Columbia (Russell, 

 1954) to southwest Texas (Wilson et al., 1952), and possibly to 

 central Mexico (Fries, Hibbard, and Dunkle, 1955). A few frag- 

 ments are known from New Jersey (Wood et al., 1941, p. 31 ; Gazin, 

 1953, pp. 8, 34). The better and more diversified Eocene assemblages 

 are in the Rocky Mountain states and in California. 



Oligocene mammals are known from sites in the central part of 

 western North America: from the northern Great Plains to Cali- 

 fornia, from southwestern Saskatchewan (Russell, 1940) to south- 

 western Texas (Stovall, 1948). Best Oligocene assemblages are from 



