268 TYPES OF ANIMAL LIFE 



in order to see if there we can find evidences such as do 

 not exist in the living world, to guide us in our quest. 



In the first place, it may be mentioned that, in the 

 latest tertiary cavern- deposits of Brazil, and in the 

 vicinity of Buenos Ayres, remains have been found of an 

 enormous kind of armadillo, which differed greatly from 

 all existing armadillos. Its bony coat was entire, 

 reaching from the neck to the root of the tail, without 

 the interposition of even a single movable band ; the tail 

 was also enclosed in a strong bony sheath. Many 

 varieties of these animals, known as Glyptodons, once 

 existed, and some have left their remains not only in 

 Mexico, but also in Texas. But though these animals 

 diverge in structure from existing armadillos, they do 

 not diverge from them in the direction of the sloth, but 

 rather in carrying to a still higher degree the characters 

 of the armadillo type. This makes them especially 

 interesting, because, as a rule, the animals which are 

 most recent are most specialised, while earlier forms are 

 more generalised in their organisation. Such was by no 

 means, however, invariably the case, and we have a 

 remarkable instance to the contrary, in the sabre-toothed 

 tigers, which, as is shown in our article on the racoon 

 carried the carnivorous organisation to a higher degree of 

 specialisation and perfection than do any tigers, lions, or 

 other members of the cat-tribe which exist in our own 

 day. Not only, indeed, did these ancient armadillos 

 have a shell or carapace in one solid piece, but the back- 

 bone, instead of consisting of a series of distinct bones 

 (vertebra) separated by joints, had their vertebrae almost 

 entirely fixed together into one solid bony tube, con- 

 taining the spinal marrow, with one complex joint at the 

 base of the neck to allow of the head being withdrawn 

 within the shelter of the carapace. 



