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SCIENCE 



[N. S. Vol. XLIII. No. 1100 



directly or indirectly connected witli one 

 another, though it is not necessary to sup- 

 pose that these connections all existed at 

 t^e same time. In the Cretaceous Period 

 every continent, even Australia, had its 

 Dinosaurs, huge, slow-moving, land rep- 

 tiles, which could not have crossed wide 

 arms of the sea, but were dependent for 

 their spread upon continuity of land. It 

 may likewise be assumed that the minute 

 and primitive mammals of the Mesozoic had 

 a similar, world-wide distribution, though 

 the data are still too scanty to permit any 

 positive statements with regard to them. 

 Early in the Tertiary Period of the 

 Cenozoic Era, South America was com- 

 pletely cut off from any land communica- 

 tion with North America, assuming that 

 such communication had previously existed, 

 as it probably had. Thenceforward and 

 for a very long period of time, the faunas 

 of the two American continents developed 

 in entire independence of each other and 

 with remarkably different results. 



To the student who is familiar with the 

 Oligocene and Miocene mammals of the 

 northern hemisphere, it is like entering a 

 new world, when he begins to examine the 

 mammalian faunas of the Deseado and 

 Santa Cruz formations of Patagonia. In 

 any comparison between the homotaxial 

 faunas of North America and Europe, the 

 differences are in species and genera, less 

 commonly of families, but between South 

 America and the northern hemisphere it 

 is mainly a difference of orders. These 

 Patagonian faunas contain no Carnivora, 

 Artiodactyla, Perissodactyla or Probos- 

 cidea, the groups which were most abundant 

 in Arctogsea. Beasts of prey were numer- 

 ous and varied, but they were all pre- 

 daceous marsupials; two other groups of 

 marsupials, the opossums and coenolestids, 

 were also common, at a time when the whole 

 order had vanished from the northern 



hemisphere, apparently even from North 

 America. An extremely abundant, di- 

 versified and conspicuous element of the 

 fauna, especially in the Santa Cruz and 

 subsequent formations, was the character- 

 istic South American order of the Eden- 

 tata, which included the ground sloths, ar- 

 madillos and glyptodonts, none of which 

 appeared in the northern hemisphere till 

 a long subsequent period, with the doubtful 

 exception of the armadillos. True sloths 

 and anteaters have also been reported by 

 Ameghino from the Santa Cruz, and al- 

 though the evidence for this determination 

 is insufficient, it is altogether probable that 

 these groups were already in existence in 

 the forested regions of the north, if not on 

 the plains of Patagonia, which would seem 

 to have had but few trees at that time. At 

 aU events, arboreal animals are rare or 

 absent from the fauna. 



The very large assemblage of hoofed ani- 

 mals all belonged to groups which are now 

 altogether extinct and no member of which 

 has ever been found outside of South and 

 Central America, the toxodonts, typotheres, 

 homalodotheres, astrapotheres and litop- 

 terns, a wonderful series, which took the 

 place of the hoofed mammals of Arctogasa 

 and would appear to have been strictly 

 autochthonous. Aside from the Insectivora, 

 which, as being of great geological antiquity 

 and nearly cosmopolitan in their distribu- 

 tion, have little bearing on the problems 

 with which we are now concerned, only 

 two mammalian orders occurred in the 

 Santa Cruz fauna which at the same time 

 existed in the northern hemisphere, the ro- 

 dents and the monkeys. The remarkably di- 

 versified and numerous rodents all belonged 

 to the Hystricomorpha, or porcupine-group, 

 of which North America never had a repre- 

 sentative until the coming in of the great 

 immigration from the south and to-day has 

 only the short-tailed porcupine. South 



