MARSUPIALS 139 



ratio holds; and this is very striking, for in the Santa Cruz 

 beds, the next later land deposits in this same region, more 

 than half of all the animals found are edentates belonging 

 to the armadillo, sloth, etc., families, while in the Pyro- 

 therium beds there are scarcely fifteen specimens of these 

 typical South American forms; though from the large num- 

 ber of plates in the covering of an armadillo it is always 

 probable that one or two will come to light, there being 

 thus over twice as many probabilities of an armadillo find 

 as of any other group, for they have over twice as many 

 bones to an individual. 



There are over one hundred rodent jaws, of some eight 

 different species, all belonging to typical South American 

 families. They are not far different from the Santa Cruz 

 forms, and these all belong to families still confined to 

 South America; or, in the case of the porcupine, migrants 

 from that continent in comparatively recent times. We 

 have ancestral members of the porcupine family, the 

 Guinea pig, and the cane rats, which offer no connections 

 with any other group which would explain whence they 

 came. 



Carnivorous forms are rare, but there are a few forms 

 which lived by preying on other animals, and these all 

 belong to the extinct group of Sparsodont marsupials. 

 This presence of marsupials has caused a theoretic con- 

 nection with Australia, by way of the Antarctic continent; 

 but the relationship is so distant and the difficulties in 

 the way of that connection so great, that it seems much 

 simpler to look in some other direction for the origin of 

 these forms, especially as during the Cretaceous this ancient 

 group was already spread over North America and Europe, 

 the members of the group being on these two continents 

 even as early as in the Jurassic; so that it would be more 

 natural to feel that the same migration which introduced 

 the earliest ungulates brought also the marsupials. As 

 suggested above, this may have been from Africa during 



