102 PRIMITIVE UNGULATA CHAP. 



possess of earlier mammals, we must arrive at the general con- 

 clusion that two of the existing larger groups of the Eutherian, 

 non-Marsupial, mammals were differentiated at quite the begin- 

 ning of the Eocene, and were represented by forms from which 

 it is possible to derive at least the existing Carnivora, Insectivora, 

 Artiodactyla, and Perissodactyla. These were the Creodonta and 

 the Ungulate Condylarthra. In addition to these we may 

 enumerate as very early types the Lemuroidea, represented by 

 such forms as Indrodon in the New World, and (though later) by 

 Necrolemur, etc., in the Old World, and the Edentata, if we are 

 to allow as their ancestors the Ganodonta. 



The early Eocene strata also contain representatives of at 

 least one order, the Amblypoda, which increased subsequently, 

 but has died out without descendants, unless we are to believe 

 with some that the Elephants are to be derived from these 

 Eocene " pachyderms." In later Eocene times the great majority 

 of the existing orders, and even subdivisions of orders, are to be 

 met with ; and there are in addition such totally extinct orders 

 as the Typotheria, Ancylopoda, and Tillodontia. Coupled with 

 this gradual specialisation in the orders of Eutherian mammals, 

 there is naturally a vast increase in the number of generic and 

 family types. This culminates perhaps in the Miocene, from 

 which time there has been a gradual decline in mammalian 

 variety, so that it is justly said that we live now in an epoch 

 which is impoverished of mammals. This gradual decay has 

 persisted until to-day, as is witnessed by the extinction of the 

 Ehytina and the Quagga, and the growing rarity of the White 

 Ehinoceros and the American Bison. 



The early Eutherian stock consisted of small mammals 

 with small heads and slender, long tails. The limbs were 

 pentadactyle, ensheathed in claws or broader hoofs. The fore- 

 limbs may have been partly prehensile. The teeth were forty- 

 four, completely differentiated into incisors, canines, molars, and 

 premolars ; and there appears to have been a complete diphy- 

 odontism. The canines were not greatly enlarged, and no 

 diastema separated any of the teeth. The molars were bunodont 

 or of a more cutting pattern, with some five or six tubercles. 

 These animals were, moreover, very small-brained. This early 

 stock is represented by Creodont and Condylarthrous animals, 

 the exact boundaries between which are hardly marked in the 



