“Teeth,” the young paleontologist answered. “It wouldn’t be a wolf, Mr. Round-up Dick, because a wolf eats flesh and his teeth are made sharp for tearing. A horse or a rhinoceros lives on grasses and plants and he has flat teeth to grind his food. You can tell almost any kind of animal at once by one tooth, and if you have all the teeth of the lower jaw, you can tell a great deal about the animal. Suppose that I found a jaw, I could tell by the teeth what food that animal lived on. If I knew what food he ate, I could tell whether he lived on the plains, or in a forest or in a swamp. If he lived on the plains, I would know that he must have been able to run fast; if he was in the forest, that he would be heavy; if in the swamp that he must have been able to swim. You see, if I found a jaw alone, I could give you a good idea of the animal.” The cowboy stared at him in blank astonishment. “And in this case,” Antoine continued, “I can see the feet as well. And the foot tells all about the animal’s habits. If I find teeth made to crop grass, and light feet made to run quickly over the grass, I do not have to be very clever to see that such an animal lives on a grassy plain. And if I find that in one part of the world the animal with teeth for eating grass did not develop feet to travel swiftly with, while in another part of the world it did, I do not have to think very hard to see that in the place where the animals did not become swift they had no swift-running enemies, while in the other place they did. So you see, Mr. Round-up Dick, where the grass-cropping animals had feet that did not make them swift, I should not look for swift-running enemies, such as the American sabre-tooth tigers.” “It’s all so plumb easy when you talk,” said the range-rider, “but I’d ha’ fought, bled, an’ died among a pile o’ bones before I’d ever ha’ thought it out.” “Have you got pretty good teeth, Dick?” Perry asked. “I c’n bite nails,” the cowboy answered. “All right,” rejoined the boy, opening his mouth and pressing his thumb against his teeth. “Suppose you count them. Begin in the middle. You’ve got two teeth shaped like chisels, haven’t you, and then comes a sharp one, like the long teeth of a dog? And behind they’re all fairly flat, eh?” “You call the turn!” “Now, Dick, a dog has three chisel-shaped or incisor teeth, while a cow has three in the lower jaw and none in the upper jaw. Then behind that the dogs have jagged or sharp-cutting teeth, while a cow’s teeth are all more smooth. If Antoine says that’s a rhinoceros type, it can’t have any sharp-cutting teeth like those of a dog; a rhinoceros doesn’t eat flesh, and so he doesn’t need flesh-tearing teeth to tear with. A rhinoceros browses, and so his teeth are grinders to mash the vegetation to a pulp.” [Illustration: _Courtesy of American Museum of Natural History._ SMILODON, THE SABRE-TOOTH TIGER. One of the most ferocious of the animals against which Primitive Man had to fight his way.]