“I’d awfully like to go there,” said the boy, “but I do think I ought to finish up the Pteranodon first, and it’ll take me all of two weeks. I’ll join you out at Haystack Butte, if I may. I’d like to go with you to see that mammoth, though, ’cause I’ve never seen one really in the ground. And just what sort of a beast was the Columbian Mammoth, Uncle George? I’ve never got clearly in my head the differences between a mastodon and a mammoth.” “It’s a thing you ought to know,” his uncle said, “particularly as you found the Moeritherium for us. You remember the Paleo-mastodon skull that Antoine found the night before you made your discovery, don’t you?” “Of course!” “And you remember that while the Moeritherium skull was found in an Upper Eocene bed, the Paleo-mastodon skull was found in a lower Oligocene.” “Of course.” “And you just now told me that Africa was an island during the Eocene period and that it gradually rose, making land bridges across the Mediterranean during the later Oligocene.” “Yes,” Perry agreed. “Very good. Then, when the land bridges were made, and the mammals from Africa first had the chance to make their way into Europe and Asia and so on to America, the ancestors of the elephants were a little more advanced than Paleo-mastodon. That’s clear?” “Quite.” “And so you might find the descendants of Paleo-mastodon in Europe in the Miocene Period, after the land bridges were made, but not earlier.” “Yes, I see.” “That’s exactly what happened. In the Lower Miocene of Europe is found the Trilophodon or four-tusked Mastodon. The European form is older and less developed than the four-tusked Mastodon of America, but the little fellow traveled from Africa to China, going through Arabia, and from Africa to Florida by way of the Behring Straits land bridges. They weren’t straits, then, of course. “So, in that warm corner of Africa, the elephants slowly began to develop until the time of Paleo-mastodon and later, going on their own way without any interference from others. They managed to defend themselves from the creodonts and, little by little, developed trunks and tusks. Then came the land opening into Europe and Asia, and, like a stream bursting through a dam, the four-tusked Mastodons scattered to the four corners of the earth, trumpeting as they went. “They grew more and more powerful. Soon the little four-tusked fellow decided to give all his attention to the development of his upper tusks and to let the lower ones go. One type, which we call the Beaked Mastodon, had a short jaw and his lower tusks turned down. It wasn’t a very good arrangement and his kind became extinct. The other two types are distinguished by a difference in the teeth—” “Teeth again!” exclaimed Perry.