SUMMARY OF AFFINITIES AND ORIGIN 663 



1. The Insectivora, Solenodon and Nesophontes, of very ancient arrival^ 

 p'robabl}^ early Tertiary, and apparently of North American origin. 



2. The gronnd-sloths, Megalocnus, Mesocnus, Miocnus, Microcnus in 

 Cuba and Acratocnus in Porto Eico, of moderately ancient arrival, prob- 

 ably late Miocene or early Pliocene, and of undoubted South American 

 origin. The rodents, with the exception of Capromys, fall also into this 

 category. 



3. The peculiar groups of birds, bats, and lizards are also no doubt of 

 comparatively ancient arrival, but their source is unknown, as we know 

 nothing of the Tertiary distribution of related groups on the mainland. 

 The modern distribution of such related groups can not be relied on, for 

 we know that among terrestrial mammals various groups which are today 

 exclusively or chiefly Neotropical were Nearctic until the end of the Ter- 

 tiary and unknown in South American faunas until the late Pliocene. 

 Presumably corresponding changes in distribution have occurred among 

 the bats, birds, and reptiles, but we have no records as to what groups were 

 affected. The Cuban crocodile may also be placed in this category. 



4. Of the two chelonians the giant tortoise may be placed as more prob- 

 ably of North American than of Central or South American origin, but 

 its time of arrival can hardly be estimated until its relations to the con- 

 tinental Tertiary species are known. The terrapin is almost certainly 

 of North American origin, derived from the Southeastern States, and of 

 comparatively late arrival, probably late Pliocene or Pleistocene. 



5. Capromys and Geocapromys are undoubtedly of South American 

 derivation, like the other rodents ; but, so far as may be judged from their 

 comparatively near affinity Avith the Venezuelan Procapromys, are of later 

 arrival, perhaps late Pliocene or Pleistocene. 



It appears, therefore, in sum, that the vertebrate fauna, fossil and 

 recent, represents only a few selections from the continental faunas of 

 eitlier North or South America; that it falls into several groups of divei'se 

 origin, and judging from their degree of differentiation, of diverse times 

 of arrival. 



Is THE INCOMPLETE AND UNBALANCED CHARACTER OF THE FaUNA 



Eeal or only Apparent? 



In the absence of hoofed animals, which form the greater part of all 

 continental fauna^, in the tendency of races normally of small size to 

 assume relatively large size and importance, in the relative fragility, so 

 to speak, of tlic fauna, leading to its early disappearance wlien man 

 * invades the region — in many further points of detail — it parallels tlic 

 faunas of those islands Avhich lie bevond the continental shelf, and diifors 



