112 ECOLOGICAL FOUNDATIONS OF ZOOGEOGRAPHY 



ing one upon the other, would push the earlier forms further and 

 further to the south. Here and there, under the protection of specialized 

 habits, or on account of barriers, remains of the primitive forms would 

 be left behind as "relicts," but in the main they would be driven to 

 the southern extremes of the three southern land masses, where they 

 would be preserved most effectively when the appearance of barriers 

 prevented the later, more advanced, competitors from following them. 

 This is especially notable in Australia, which has been cut off since 

 the Jurassic. It is not at all implied that advances in organization took 

 place only in the north ; favorable modifications may have arisen and 

 adaptive radiation has occurred in various other areas, but the condi- 

 tions for advance were most favorable in the north, as far as terrestrial 

 animals are concerned. 



Primitive southern forms. — There is a great accumulation of evi- 

 dently primitive and ancient forms in the southern hemisphere. 41 

 Australia leads in this respect with its monotremes and marsupials, and 

 with the small rodents whose only relatives exist as relicts on the 

 mountains of Celebes, Borneo, and the Philippines. 42 South America 

 has its primitive marsupials, edentates, hystricomorph rodents; its 

 tinamous among the birds and the iguanid lizards. Africa south of 

 Sahara has preserved primitive mammals such as the tragulids 

 (Hyaemoschus) , the lemurs, the aardwolf (Proteles), and the golden 

 mole (Chrysochloris). In Madagascar the lemurs and centetids are 

 primitive; the viverid genus Eupleres is intermediate between other 

 genera and, as such, is primitive; the bird genus Mesites seems to be 

 the most primitive member of the crane and rail group. 43 Primitive 

 groups of invertebrates are also especially abundant in the southern 

 hemisphere. Among insects, the most generalized type of termites 

 occurs in Australia, the simplest Lepidoptera, resembling Trichoptera, 

 are found in Australia and New Zealand, and about half of the 

 Australian bees belong to the primitive genus Prosopis. Taylor 44 has 

 shown that the most primitive land snails, Helicidae, are found in 

 the southern continents and in New Zealand, and that progressively 

 more advanced species are found in the north. The whole mollusk 

 fauna of South Africa may be characterized as a primitive one. The 

 distribution of earthworms is similar in its arrangement, with primi- 

 tive forms in the southern hemisphere, advanced forms in the northern. 



Discontinuous distributions, with the most varied arrangement of 

 the respective isolated areas, are the rule in the southern land masses. 

 The most primitive of the living odd-toed ungulates, the tapirs, are 

 found in Malaya and South America. The dwarf deer (Tragulidae) 

 are found in the East Indies, in southeast Asia, and in West Africa. 



