354 AN ELEMENTARY TEXT-BOOK OF BIOLOGY. 



No fossil forms are found elsewhere, so that the place of origin 

 of this order is unknown. 



2. Marsupialia. Consists of eight families (comprising thirty- 

 seven genera), of which only one, the Opossum family (including 

 three genera), occurs outside the Australian region. The Opossums 

 are Neotropical and Nearctic. 



Fossil opossums occur in the Pleistocene of America, and in 

 much older European deposits (Eocene to Miocene). The secondary 

 rocks of Europe contain a number of small forms, which probably 

 resemble the ancestors of the Australian Marsupials. We may 

 therefore suppose that this order originated in the Palsearctic 

 region, and then extended into what is now Australia (at that 

 time united by land with Asia), isolation occurring soon after, 

 followed by specialization in various directions. The Opossums 

 seem first to have existed in Europe, from whence they spread 

 into America by former northerly land-connections. 



3. Edentata. This order is now chiefly limited to S. America, 

 but Orycteropus is peculiar to the Ethiopian region, while Manis 

 is found both in that and the Oriental region. 



The geological evidence is in favour of considerable development 

 in Africa, whence the order would spread north to the Oriental 

 and Palsearctic regions, and thence on to America. The compe- 

 tition with higher forms has caused its extinction in most areas, 

 and Edentates appear to be most abundant in S. America, because 

 the competition with other animals is there comparatively small. 

 The peculiar burrowing or climbing habits of most of the genera 

 also tend to preserve them, and these habits no doubt represent 

 attempts to escape from the severe competition with higher forms. 

 The size of existing Edentates is insignificant compared with that 

 of Pleistocene S. American and European genera. 



4. Ungulata. (a) Artiodactyla. Non-ruminantia. Swine are 

 only represented in America by peccaries (Dicotyles) ; true swine 

 are found in all the other regions, but only extend into the 

 Australian as far as New Guinea. These animals are first known 

 in the European Eocene, and during Miocene and Pliocene times 

 were as common in N. America as Europe, but since then have 

 almost entirely disappeared from the former area. 



The hippopotamus is now limited to the Ethiopian region, but 

 fossil forms occur in Europe (Pliocene and Pleistocene) and India 

 (Miocene). 



