344 VERTEBRATE ZOOLOGY 



gradual elimination. Only a very few of the archaic mammals sur- 

 vived beyond Eocene times and these were rather generalized types, 

 suitable to be the ancestors of the modernized mammals. There was 

 probably considerable emigration on the part of certain of these sur- 

 viving archaic types. It may well be, for example, that the marsupials 

 of Australasia were the descendants of a very early group of multi- 

 tuberculate mammals that succeeded in reaching the Australasian 

 peninsula before it was cut off from the Asiatic continent. The 

 cutting off of the Australasian land bodies must have occurred before 

 the modernized mammals reached that part of the world, for there 

 are in those regions no true modernized mammals. 



Origin op the Modernized Mammals 



The modernized mammals include practically all existing placental 

 mammals and their immediate ancestors, including: true carnivores, 

 rodents, odd- and even-toed ungulates, elephants, sirenians and whales. 

 To this list some authors would add edentates, bats, and insectivores. 

 "In contrast with the archaic mammals," says Lull, "the 

 modernized types are all creatures of high potentiality, and, 

 where they became extinct, were rather the victims of circum- 

 stance than creatures that died because of lack of adaptability, 

 although certain groups seem to have run a natural course and 

 their extinction was heralded by evidences of racial senility. 



"As the archaic forms were characterized by lack of progressive 

 brain and feet and teeth, so the modernized races were distin- 

 guished by the possession sometimes of one (primates), some- 

 times of two (elephants), again by all three (horses) of these 

 destiny controlling organs, but in general the modernized animals 

 were progressive, highly adaptable forms." 

 Place of Origin. — It is believed that the modernized mammals 

 originated in the great Arctic Continent. The reasons for this belief 

 are: first, there is a striking resemblance between the first European 

 and the first North Anierican modernized mammals; second, palaeo- 

 geographers tell us that a fluctuating land bridge between the eastern 

 and western continents existed from time to time, and between times 

 was submerged; third, the climate of the Arctic regions was at one 

 time warm, as is evidenced by the discovery of fossils of sub-tropical 

 plants on the coast of Greenland. 

 Time of Origin. — All available evidence seems to point to the 



