308 



SGIENGE. 



[N. S. Vol. III. No. 61. 



When we reach the Tertiary, important 

 facts become available, but, as in the earlier 

 ages, too fragmentary to be conclusive. A 

 long succession of Tertiary land faunas is 

 known only from South America. Even 

 the most cursory examination of these 

 faunas shows in the most unmistakable 

 manner the extreme isolation of South 

 America. The oldest of tlie Tertiary for- 

 mations of Patagonia, the Pyrotherium beds 

 have yielded a fauna which promises to 

 prove of the highest interest, but as yet it is 

 so imperfectly known that it cannot be em- 

 ployed in the solution of the Antarctic 

 problem. The earlier ilfiocene (Santa Cruz) 

 mammals of that continent are totally dif- 

 ferent from those of the northern land- 

 masses, so much so that the correlation of 

 horizons becomes a matter of extreme diffi- 

 culty. The hoofed animals all belong to 

 orders unknown in the north, Toxodontia, 

 Typotheria, Litopterna, and the principal con- 

 stituents of the fauna are immense numbers 

 of Edentates, Marsupials and Rodents, with 

 several platyrrhine monkeys. No artiodac- 

 tyls, perissodactyls, proboscidians, Condj'- 

 larthra or Amblypoda, neither Insectivora, 

 Cheiroptera, Carnivora or Creodonta are 

 known. The Edentates are all of the spe- 

 cifically South American type, sloths, arma- 

 dillos and the like. The Eodents also are 

 very much like those which still charac- 

 terize the region, though most of the genera 

 are distinct ; they are all Hystricomorpha, 

 neither squirrels, marmots, beavers, rats or 

 mice, hares or rabbits occurring among 

 them. The Primates are typically neotropi- 

 cal and evidently belong to the platyrrhine 

 group. The Marsupials are parti j' opos- 

 sums, more or less like those which still 

 inhabit the Americas, and, what is at first 

 sight very surprising, partly of Australian 

 type. The latter contain both diprotodont 

 forms {Ahderites, Acdestis Epanorthus) allied 

 to the existing Hypsiprymnus and polypro- 

 todont genera {Protoproviverra, Cladosietis, 



etc.), the affinity of which to the Dasyuridce 

 is clear. Ameghino, it is true, places these 

 latter forms in a new order, the Sparasso- 

 dontia, but this seems unnecessary and mis- 

 leading. 



The fauna of the succeeding ' Patagonian 

 formation' is of exactly the same general 

 character and contains no new elements, 

 but merely somewhat more advanced gen- 

 era of the same orders, while the Marsupials 

 are much reduced in numbers and impor- 

 tance. 



In the Pliocene (Monte Hermoso) ap- 

 pear the first traces of the union with North 

 America, in the presence of mastodons, 

 horses, tapirs, deer, llamas and true carni- 

 vores, and frorn that time till far into the 

 Pleistocene the intermigrations between the 

 two continents kept up, until a large num- 

 ber of common types had been established. 



The curious composition of the South 

 American mammalian fauna in Tertiary 

 times presents us with some very well-de- 

 fined but extremely difficult problems. (1.) 

 How is the pi-esence of groups to be ex- 

 plained, which have a clear relationship to 

 those belonging to the Northern hemi- 

 sphere, namely the Primates, Ungulates and 

 Eodents ? An easy short cut out of the 

 difficulty would be to assume that the re- 

 lationship is only apparent and due to con- 

 vergent development. It is, of course, pos- 

 sible that such is the true explanation, but 

 it is most unlikely, and in the absence of any 

 evidence in its favor we need not stop to 

 discuss it. Much more probable is it that 

 these groups point to some connection, di- 

 rect or indirect, with the northern hemi- 

 sphere, either in late Mesozoic or early 

 Tertiary times. One would naturally ex- 

 pect to find that this connection was by 

 way of North America, but there are grave 

 difficulties in the way of such a view. As 

 we have seen, the indigenous South Ameri- 

 can rodents were all hystricomorphs, and 

 while this group is represented in Europe, 



