IV EARLY TERTIARY MAMMALS IOI 
be devoid of mammalian remains. This gap, however, has been 
filled up by the discovery of mammalian remains in the North 
American Laramic formation, which seems to be clearly of Creta- 
ceous age. Furthermore, it is held by some that the Purbeck beds 
are more properly to be placed with the Cretaceous, which would 
then necessitate the consideration under the present heading of 
some of the types already dealt with; and if, as 1s suggested in 
the following section, the lowest so-called Eocene beds are really 
referable to the Cretaceous, there is no lack of mammalian remains 
in that period. And, moreover, it was in that case the Creta- 
ceous period which witnessed the evolution of the existing orders 
of Placental mammals. Otherwise the mammalian remains of the 
Cretaceous agree with those of the Jurassic. We find remains 
of the Multituberculata in fragments of Plagiaulacidae and 
Polymastodontidae. Péilodus is a genus which has two pre- 
molars; and AMZeniscoessus 1s another multituberculate from the 
same Laramic formation. The other detached fragments of 
mammals are thought by Osborn to represent both Placentals 
and Marsupials. 
The Mammals of the Tertiary Period.— Unless the lowest 
beds of the earliest Tertiary period, the Eocene, such as the 
Torrejon of North America, should be in reality referred to the 
Cretaceous, there is no evidence that the modern groups of 
Mammalia existed before the present epoch of the earth’s history. 
It is probable, however, that the Eutheria as a group were Meso- 
zoic. ‘The fossil jaws that have been considered in the last chapter 
may quite probably be primitive Eutherians, or even divisible, as 
believed by Professor Osborn, into Marsupials and Insectivores. 
In the Tertiary, however, apart from the question as to the 
nature of the Puerco and Torrejon formations, and as to certain 
South American strata whose fossil contents have been investi- 
gated by Professor Ameghino, we find the first traces of mammals 
definitely referable to existing orders, or to be distinctly com- 
pared with existing orders. Since, however, representatives of 
types which have obvious relationships to modern types appear 
in considerable profusion in the very earliest strata of the 
Kocene, it seems clear that much remains to be discovered in 
beds earlier than these. Confining ourselves, however, to facts 
and to comparisons which can be made on more than a few 
lower jaws and scattered teeth, which is practically all that we 
. 
