OF MAMMALIA. 599 
But one of the most extraordinary discoveries with regard to this 
realm is the fact that it has had a great past history. The fossils teach 
us, firstly, that the Xexarthra at one time were so numerous and attained 
such large dimensions as to form quite the leading feature of the realm. 
The giant ground-sloth or Megatherium and its near ally the AZylodon 
are found in the Pleistocene and Recent, whilst the equally ponderous 
Glyptodons or giant armadillos occurred at about the same period. 
These Edentata as a group appear to have extended back at least as far 
as the Miocene, if not the Oligocene, and at present we have no good 
evidence that Edentata have ever occurred in other parts of the world, 
with the reservation that one or two types appear to have made their 
way into North America during the Miocene epoch, just as some arma- 
dillos have done at the present time. 
: The second lesson learnt from the fossil beds is that the peccaries, 
vicufias, guanacos, deer and tapirs which now form the very sparse 
tepresentatives of the great order Ungulata, and the Carnivora are all 
comparatively recent immigrants from the North, no trace of any of 
them occurring below the Pliocene of Neogcea, though abundant remains 
are found in North America. On the other hand, there appears to have 
been a very rich ungulate fauna during the past, though they in their 
turn may have originated in the North and migrated southwards. How- 
ever that may be, the horse flourished here in Pleistocene times, as also 
the Mastodon, both probably northern immigrants. In addition, there 
were from the Miocene onwards an enormous number of strange ungu- 
lates, some like rhinoceroses in size and other features. At least four 
entirely peculiar sub-orders of the Ungulata have to be instituted to 
hold these extinct forms. 
The Carnivora, for the same reasons as stated above, appear to 
have been comparatively recent immigrants from the North, like the 
peccaries and others. We therefore have a considerable light thrown 
upon the past history of Neogcea which enables us, at any rate to some 
extent, to explain its peculiarities at the present day. Put succinctly 
the history of events appears to have been as follows :—The land-union 
between North and South America appears to have been of recent date, 
and from some unknown time up to at least the close of the Miocene 
epoch, the two continents were separated by the sea. South America 
then had its peculiar fauna of abundant Zdentata and Ungulata, 
differing from any other part of the world, but upon the establishment 
of the land connection between the two continents the Neogoean 
realm was flooded with up-to-date immigrants from the north. Vicufias 
and guanacos, ‘‘cats” and “dogs” (Feléde and Canide), raccoons and 
skunks, deer, horses, peccaries and mastodons, opossums and many 
rodents rapidly spread over the land and may have contributed consider- 
ably to the extermination of many of the indigenous types. Through 
the Pliocene and Pleistocene this hybrid fauna flourished until all the 
larger types were for some unknown reason exterminated and the present 
fauna remained. 
But we still have the indigenous fauna of Neogcea and cannot help 
attempting to trace its origin. Whence arose all the primitive Ungulates, 
the Edentates, hystricomorphous rodents, the monkeys and the mar- 
supials other than opossums (opossum-rats and fossil allies in the 
