594 EDENTATES xxn. 4- 



insectivoran stock very early (p. 601). The South American ant- 

 eaters form a natural group with the armadillos and sloths, having, 

 like the South American ungulates and other animals, proceeded along 

 several courses of evolution of their own during the long isolation of 

 their continent throughout the Cenozoic period. The term Edentata is 

 now reserved for this South American group. 



In many ways the Edentata remain close to the basic eutherian 

 condition. The characteristic feature has been a simplification of the 

 teeth, which are absent altogether in the ant-eaters themselves. In 

 sloths and armadillos the front teeth are absent and the hinder ones 

 are rows of similar pegs, with no covering of enamel. Except in sloths, 

 there is considerable elongation of the snout and the whole cranium 

 is of tubular form, with a low brain-case, containing a small brain with 

 poorly developed hemispheres, having a large olfactory region. The 

 jugal bar is often incomplete, but the hind end of the jugal carries a 

 large downward extension in sloths and ground sloths. A characteristic 

 common to all the Edentata is the presence of extra articulations be- 

 tween the lumbar vertebrae, a striking feature in view of many different 

 modes of locomotion in the group. From these articulations the group 

 gets its name, Xenarthra. Several other peculiar features of the 

 skeleton are common to most or all these animals, such as a fusion of 

 the coracoid with the acromion to enclose a coracoscapular foramen 

 and a union between the ischium and the caudal vertebrae. The feet 

 have well-developed claws, often used for digging, and the animals 

 may walk on the outside of the claws, though some species are arboreal 

 and use the claws for hanging. 



Many of the characteristics of the group are obviously those of all 

 generalized eutherians, the edentates having departed little from the 

 original mammalian plan. For example, they all have rather low 

 temperatures, fluctuating widely with the environment. Their features 

 are mostly the result of special ways of life, often leading to bizarre 

 external appearances, such as the long snout of the great ant-eater or 

 the carapace of the armadillo. 



The order Edentata is divided into two suborders, the first *Palae- 

 anodonta for a few Palaeocene and Eocene types such as *Meta- 

 cheiromys, which had not yet acquired the structure of the vertebrae 

 found in all the remaining edentates (suborder Xenarthra). The 

 palaeanodonts are found in North America and are held by some to be 

 survivors of the original stock, existing before the separation of the 

 continents. The xenarthrous population itself split up early and we 

 can recognize two main groups (infraorders), the Cingulata for the 



