102 ESSAY ON CLASSIFICATION. Part I. 



SECTION XXII. 



LOCALIZATION OF TYPES IN PAST AGES. 



The study of the geographical distribution of the animals now living upon 

 earth has taught us, that every species of animals and plants has a fixed home, and 

 even that peculiar types may be circumscribed within definite limits, upon the 

 surface of our globe. But it is only recently, since geological investigations have 

 been carried on in remote parts of the world, that it has been ascertained that 

 this special localization of types extends to past ages. Lund for the first time 

 showed that the extinct Fauna of the Brazils,^ during the latest period of a past 

 age, consists of different representatives of the very same types now prevalent in 

 that continent; Owen has observed similar relations between the extinct Fauna 

 of Australia^ and the types now living upon that continent. 



If there is any naturalist left who believes that the Fauna of one continent 

 may be derived from another portion of the globe, the study of these facts, in 

 all their bearing, may undeceive him. 



It is well known how characteristic the Edentata are for the present Fauna 

 of the Brazils, for there is the home of the Sloths, (Bradypus,) the Tatous, 

 (Dasypus,) the Ani^eaters, (Myrmecophaga) ; there also have been found those 

 extraordinary extinct genera, the Megatherium, the Mylodon, the Megalonyx, the 

 Glyptodon, and the many other genera described l^y Dr. Lund and Professor 

 Owen, all of which belong to this same order of Edentata. Some of these 

 extinct genera of Edentata had also representatives in North America, during the 

 same geological period,^ thus showing that though limited within similar areas, the 

 range of this type has been different in different epochs. 



Australia, at present almost exclusively the home of Marsupials, has yielded 

 also a considerable number of equally remarkable species, and two extinct genera 

 of that type, all described by Owen in a report to the British Association, in 

 1844, and in Michell's Expeditions into the Interior of Australia. 



1 Lund, (Dk.,) Blik paa Brasiliens Dyreverden of Extinct Mammalia, Ann. and Mag. Nat. Hist., 1846, 

 for sidste Jordomvasltning. K. Danske Vidensk. vol. 17, p. 197. 



Selsk. Afhandl. VIII., Kiobenhavn, 1841, 4to. fig., p. ' Leidy, (.Jos.,) A Memoir on tlie Extinct Sloth 



61, etc.; Engl. Abstract, Ann. and Mag. vol. 3, p. Tribe of North America, Smitbson. Contrib. 1855, 4to. 



422. fig- — Wyman, (J.,) Notice of Fossil Bones, etc., Am. 



2 Owen, (R.,) On the Geographical Distribution Journ. Se. and A., 2d ser., 1850, vol. 10. 



