xxii. 5 ARMADILLOS 595 



armadillos and glyptodons, and Pilosa for the ant-eaters, sloths, and 

 ground sloths. 



5. Armadillos 



The armadillos (Dasypodidae) (Fig. 371) have departed least from 

 the ancestral plan and are a very ancient group, already differentiated 

 in Palaeocene times. They are nocturnal and fossorial and obtain 

 protection by the development of bony plates in the skin, these being 



\Mku; 





Fig. 371. Hairy armadillo, Dasypus. (From photographs.) 



Fig. 372. Glyptodon. (From a reconstruction lent by the Trustees of the British Museum.) 



covered by horny scutes. The plates are usually arranged in rings 

 round the body and in some genera they allow the animal to roll up 

 into a ball. The vertebrae tend to be fused to support the shield, and 

 many vertebrae unite in the sacrum. The teeth are simple uniform pegs, 

 without enamel, and with open roots and continuous growth. They are 

 often more numerous than in other mammals (as many as twenty-five 

 in each jaw); with simplification of the system of tooth morphogenesis, 

 repetition becomes possible, as we see also in whales. The armadillos 

 are insectivores and omnivorous scavengers in tropical Central and 

 South America ; there are many different genera and species. The nine- 

 banded armadillo (D. novemcinctatus) is a very active burrower and is 



