DISTRIBUTION 131 
independently of the mouth and gullet, thus averting the danger of 
suffocation while the milk is passing down the latter passage. 
Distribution.—The existing species of Marsupials are, with the 
Fic. 35.—Front view of skull of Surcophilus ursinus, showing polyprotodont and carnivorous 
dentition (Quart. Journ. Geol. Soc. vol. xxiv. p. 313). 
exception of one family (the Didelphyide), limited in geographical 
region,! 
distribution to the 
mammalian fauna of Australia, 
New Guinea, and some of the 
adjacent islands. The Didel- 
phyide are almost purely Neo- 
tropical, one or two species 
ranging northwards into the 
Nearctic region. Fossil re- 
mains of members of this 
family have also been found in 
Europe and America in strata 
of the Eocene and early Mio- 
cene periods ; and it is probable 
that at least many of the poly- 
protodont Mesozoic mammals 
noticed in Chapter IV. are 
referable to the Marsupialia. 
Classification.—In dividing 
the Marsupials into minor 
groups, it may be observed 
that one of the most obvious 
distinctive characters among 
Australasian 
forming the chief 
Nun 
Fig. 36.—Front view of skull of Koala (Phas- 
colarctus cinercus), showing diprotodont and 
herbivorous dentition (Quart. Journ. Geol. Soc. 
vol. xxiv. p. 313). 
them is derived from the form and arrangement of the teeth. 
1 Including the transitional Austro-Malayan region. 
