FOSS/L RODENTIA 37 



there.' 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 is 

 Polymastodon of the basal Eocene ; the oldest shown in the case 

 is the tiny Ctenacodon of the Jurassic period. Chirox and Ptilodiis 

 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. 



