MAMMALIA. 99 
Order EDENTATA. 
Eliminating the Old World genera Orycteropus and Manis, this order is confined to 
South and Central America. Cholepus and Bradypus, the two genera of Sloths or 
Bradypodide, pass from South into Central America, the former as far as Costa Rica and 
the latter to Nicaragua. Myrmecophaga and Cyclopes, two of the Anteaters (Myrme- 
cophagide), also go as far as Guatemala; the third genus, Tamanduas, extends 
northward to Tabasco and Vera Cruz in Mexico. Of the large number of South 
American genera of Armadillos (Dasypodide) two only enter Central America, namely 
Cabassous (Lysiurus), which ranges from Brazil to Honduras, and Dasypus (= Tatu or 
Tatusia), which overlaps it both to the north and south, with au extension from the 
Argentine to Texas, just touching the latter state at Brownsville. 
The origin and centre of evolution of the Edentata is at present unknown. The 
only extinct forms that have been claimed to be their ancestors are the Txniodonts or 
Ganodonts of the Eocene of North America. Since this view has been authoritatively 
disputed, it needs no further consideration here. Of more importance, from our 
present point of view, is the mid-Eocene North American genus Metachetromys, believed 
by some to be a primitive Armadillo. It is true that the Armadillos (Dasypodide) are 
the least specialised of all undoubted Edentates, living or extinct, and no reason can 
be alleged against the likelihood of the discovery of an early type in the Eocene of 
North America, but since Metacheiromys unfortunately has few, if any, of the 
characters distinctive of Edentates as we know them, it cannot be maintained as 
established that the order is of North American origin. It may be suggested that 
their ancestors entered South America from Africa. However that may be, the 
~ evidence of fossil forms shows that South America has been the centre of evolution 
of the large number of existing and extinct genera that have been discovered. In 
South America, Armadillos (Dasypodide) date back to the Upper Miocene, the Dasy- 
podine (olim Tatusiine) themselves, which are now found in Central and North 
America, ranging from that date to the Pleistocene. Hence the presence of Dasypus 
in Central America and Texas must be assigned to northward migration. And the 
same must be claimed of the Sloths (Bradypodide) and Anteaters (Myrmecophagide). 
No extinct forms of these families have yet been discovered, but abundant remains of a 
wholly extinct group, intermediate in many respects between the two, but less specialised 
than either, have been discovered in South American Miocene and later deposits. 
These are the Ground-Sloths (Mylodontide and Megatheriide), which at a later date 
(Pliocene and Pleistocene) lived also in North America. 
Order MARSUPIALIA. 
The American Marsupials belong to two families, the Didelphyide (or Opossnms) and 
the Cenolestide. ‘The latter, represented by the two existing species of Canolestes 
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