374 VERTEBRATE ZOOLOGY 



The dentition of the toothed edentates is peculiar in that there are 

 no incisors and the teeth in the definitive condition are without 

 enamel. The testes are abdominal; the clavicle is always present; 

 there is an additional pair of zygopophyses on the posterior dorsal 

 and lumbar vertebrae. The edentates are strictly American in dis- 

 tribution and have been limited to this territory from the first. In 

 adaptive characters the three main types differ widely from one 

 another. 



Sub-Order 1. Pilosa (Hairy Edentates). — The hairy edentates be- 

 long to two quite distinct families: The Myrmecophagidae (ant-bears), 

 and Bradipodidse (sloths). 



Family 1. Myrmecophagidce (Ant-bears). — These are among the 

 strangest animals now living. They are truly edentate, have a long 

 slender snout, long sticky tongue, heavy front claws, and long, coarse 

 hair, characters that we have already found to be adaptive features 

 of the anteating type of mammal, no matter to what group it belongs. 

 Myrmecophaga tridadyla, the great ant-bear, is a large animal with a 

 total length from end of snout to tip of tail of at least seven feet. It 

 is very powerful and quite formidable when attacked. One swipe of 

 the great hooked claws has been known completely to eviscerate a 

 large dog. M, jubata (Fig. 193 A) is somewhat smaller but quite 

 similar. The Tamandua is a smaller ant-bear with arboreal habits 

 and a long prehensile tail. Cyclopes is the smallest of the ant-bears. 



Family 2. Bradipodidce (Sloths) .—The sloths (Fig. 193, B), in 

 spite of their marked external differences, exhibit many fundamental 

 resemblances to the ant-bears. They are highly specialized for ar- 

 boreal life. Their strong hooked claws which are much like those 

 of the ant-bears are used as hooks for suspending them from branches. 

 They always progress up-side-down, hanging from the under side of a 

 branch. In accord with this habitually inverted position the heavy 

 hair slopes from the belly toward the back; similarly the hair on the 

 limbs slopes from the feet towards the body. It seems likely that 

 this peculiar position of the hair serves the purpose of effectually 

 shedding the rain. An interesting fact has been discovered about the 

 hair: it is green in color, due to the presence in the hollows of the in- 

 dividual hairs of numerous cells of a green alga. This greenish color- 

 ing doubtless serves as a protective adaptation. The face of the 

 sloth is extremely flat, in very marked contrast with the elongated 

 face of the ant-bears. There are only four or five teeth in each half 



