FOSSIL RODENTIA 55 
there.t Fossil marsupials related to the existing ones of the 
same region are found in Australia; one gigantic extinct Wom- 
bat, Diprotodon, is shown in case 6. In South America in the 
Miocene strata are found remains of various carnivorous mar- 
supials and also of Rat-Kangaroos; a skull and other materials 
are shown in the collection. In the Eocene and Oligocene of 
Europe and North America, are found small jaws scarcely to be 
separated from those of the Opossum except by size. The 
primitive trituberculates of the Cretaceous period, in the table- 
case, may also have been marsupials. 
VI. MULTITUBERCULATES. 
This ancient group of mammals lived during the Age of Rep- 
tiles, and became extinct at the beginning of the Age of Mam- 
mals. Only jaws, teeth and other fragmentary remains have 
been found, and it is quite uncertain whether the group is re- 
lated to the Marsupials or to the Monotremes (Ornithorhynchus 
etc.). Some resemble the Marsupial Rat-Kangaroos, others 
mimic the Rodents in form. The largest and best known 1s 
Polymastodon of the basal Eocene; the oldest shown in the case 
is the tiny Ctenacodon of the Jurassic period. Clirox and Ptilodus 
of the Cretaceous and basal Eocene are most like the Rat- 
Kangaroos. 
VII. MESOZOIC TRITUBERCULATES. 
A number of very small and fragmentary jaws and teeth of 
Trituberculates from strata of the Jurassic and Cretaceous periods 
of the Age of Reptiles are exhibited here. They are interesting 
because they are the most ancient of mammals and show the 
method of their evolution from reptilian ancestors. Some are 
thought to be related to the Marsupials, others more nearly to 
the Insectivores, but until more perfect specimens are found, 
little can really be stated with certainty about them. Enlarged 
models of three of these specimens are shown in the case, besides 
casts and original specimens of many more. 
™ The only exceptions are the dingo, or wild dog, which was probably intro- 
duced by man and a few small rodents and bats. 
