THE DEGENERATION OF ARMOUR IN ANIMALS 125 



Pliocene Indian tortoise of the Siwaliks (Colossochelys Atlas); by 

 the giant tortoises of the Egyptian Eocene {Tcstudo Amnion), 

 of the Miocene of France (7". gigas) or of the Pleistocene of 

 Malta ; and by the related either recently extinct or moribund 

 species of giant tortoises of the Aldabra and Mascarene Islands, 

 Madagascar, South America and the Galapagos Islands. 



Among Edentate Mammals the armadillos of South America 

 furnish a close parallel to the fate of these giant tortoises — the 

 family of the unwieldy Glyptodon, 7 ft. in length, with its 

 inflexible, solid carapace, ventral buckler (in some cases) and 

 bony caudal sheath and of the related and still more bizarre 

 Dcrdicurus, reaching even 12 ft. in length, with its tail-sheath 

 expanded at the tip so as to bear a cluster of bony processes, 

 has— like Miolania— completely died out. The existing arma- 

 dillos, however, are not only much smaller in size and possess 

 no ventral armour whatever but their dorsal carapace is jointed 

 and flexible and composed of three to thirteen movable zones 

 of scutes, allowing of considerable freedom of action, although 

 their flexibility varies somewhat in the different species. Conse- 

 quently the present survivors have been able to battle success- 

 fully with the adverse conditions resulting from the union of 

 the two Americas (which was brought about by the emergence 

 of the Isthmus of Panama) and the consequent introduction of 

 higher forms, especially of Carnivores. Some of the extinct 

 armadillos (Chlamydotherium) were, however, still gigantic in 

 bulk, reaching nearly the size of a rhinoceros and actually 

 possessed a carapace with movable bands, as in the recent 

 forms ; want of sufficient suitable food, caused by a drier 

 climate, may have greatly militated against the continuance 

 of such bulky monsters. The modern armoured pangolins 

 (Manidcv) of the Old World are similarly the smaller survivors 

 of a race which was represented in the Pliocene of Samos by a 

 form (Palceomanis) three times as large as the existing West 

 African Mam's gigantea. 



Other well-known instances of the extinction of unwieldy 

 armoured creatures are to be found in the horned dinosaurs 

 {Triccratops, Sterrholophus) among reptiles and in the colossal 

 Dinoceras {Uintathcriuni) and Arsinoithcrium among Mammals, 

 although in these cases the excessive armour was confined to 

 the extraordinary horned processes of the skull. Even in recent 

 years one species of rhinoceros has become extinct and the 



