Darwin- Wallace Celebration. 79 



At 10.15. Dr. A. SMITH WOODWARD, F.R.S., V.P.L.S. 

 "THE EVOLUTION OF MAMMALS IN SOUTH AMERICA." 



THE subject of the Evolution of South American Mammals is 

 appropriate on the present occasion, because Darwin was one of 

 the pioneers in the discovery of fossil mammalian remains in the 

 Argentine pampas. During the ' Beagle ' expedition he found the 

 first evidence of the extinct ground-sloths, Mylodon and Scelido- 

 .therium, and of the strange large hoofed-animal Toxodon. Since 

 Darwin's time, our knowledge of these great quadrupeds and their 

 contemporaries has been remarkably extended; and within the 

 last 20 years their ancestry has been partially revealed by discoveries 

 in older Tertiary formations to the south in Patagonia. The problem 

 of the evolution of South American marnmal-life has thus become 

 understood, and can now be clearly stated. Like all other achieve- 

 ments in the study of fossils, it still remains a problem ; but there 

 is at least some satisfaction in having discovered the general nature 

 of the phenomena which have to be explained. 



According to our present knowledge, it appears that all the modern 

 groups of mammals have come into existence since the Cretaceous 

 period, namely, during Tertiary times. There is good reason to 

 believe that at the end of the Cretaceous period small mammals of 

 essentially the same kind were distributed over all the large land- 

 -areas. These mammals were carnivorous or mixed-feeders, with a 

 comparatively small brain ; and in every respect they may well have 

 been the direct ancestors of all the mammals of later times. Portions 

 of jaws and a few limb-bones of such mammals have been found to 

 the north of Patagonia, showing that they lived in South America 

 .as elsewhere. It is thus evident that the mammal-life of South 

 America began its career in the same way as that of the more 

 extensive continents in the northern hemisphere. As proved by the 

 geology of the Panama region, however, it so happened that South 

 America was completely separated from the northern lands during 

 the earlier half of the Tertiary period, when the main part of the 

 evolution of the mammals occurred. Their development on this 

 southern land was therefore independent of that on other continents ; 

 and the result was the production of several groups peculiar to 

 South America, some of them remarkable mimics of groups that 

 occur elsewhere. Most of these mammals became extinct when a 



