In the earlier ages of the present or last building-time, the mammals were not only numerous, but far exceeded in size any now existing. Indeed, it seems that as the type improved the more bulky forms passed away; the higher animals being less unwieldy. Still this suggestion must at once be met by exceptions: for in the case of the horse, as the model improved, the size of the animal constantly increased. The mammals had finally become world-masters, and before them the gigantic reptiles perished. For a time mammals and reptiles of equally stupendous proportions seemed to face each other, but the new type gained the victory over the old. The mammals, as well as the reptiles, had the faculty of adaptation; they seemed suited to a wide variety of conditions. They fed on fish, flesh, herbs, fruits, and fowl. Some of them had bare tough skins; others wore long scanty hair; others again were clad in fur, or heavy wool. Some of them burrowed in the ground; some lived in caves and dens; some were tree dwellers, or arboreal; others wandered over wide savannahs or in the forests, careless of other shelter than trees or reedy jungles. Next after the rat-like families came a tribe of insect-eating creatures like the present ant-eaters, but far exceeding them in size, some of them being nearly as large as a rhinoceros. The mylodon was a fruit-eater and so large and strong that it was able to tear down the trees which bore the fruit it coveted; certainly a destructive fashion of fruit-gathering, proving the mylodon much more barbarous than a Saracen.[48] Meantime, while these mammals flourished on the land there were numerous others in the sea, and these of a very large size, although no fossils have yet shown that the sea-mammals preceded those of the land. The whales and the sirens seem to have appeared many years ago, and have since continued. Enormous armadillos, covered with mail and very like the tortoise family of reptiles, marched about the woods or sunned themselves upon the shores. When twilight settled over the ancient woods and savannahs the mammals of the air came forth, and bats flew zigzagging about, hunting after insects or little birds. The bone-caves of the age before man came have abundant bones of mammals; bones which represent the pursuers and the pursued, hunters and hunted,--some the relics of the meat-eating, hunting beasts, and some, the gnawed remains of their prey.