Elephants out of the ooze

By the 1920's the evolution of elephants (proboscideans) seemed all but resolved. Paleontologists had long been familiar with mammoths and mastodons, the great shaggy beasts that had so recently gone extinct, but in 1901 fitting candidates for the progenitors of all later elephants became known. Named Moeritherium and Palaeomastodon by British paleontologist C.W. Andrews, the two proboscideans from Eocene rock of the Fayum region of Egypt were the forms that could connect elephants to the rest of the mammal family tree.

Finally elephant evolution could be presented in a straight line. It had started with the short and stout Moeritherium, a snub-nosed elephant that lived like a hippo. (Some, like H.F. Osborn, thought that it was not an elephant but a collateral relative. He regarded it as a "missing link" that only stood close to the true ancestry of elephants, but other paleontologists generally regarded it as the first proboscidean.) Palaeomastodon represented the next, more terrestrial step. As H.F. Osborn remarked in a popular description the entire skeleton of Palaeomastodon seemed "prophetic" of the multitude of elephant types that were to come.

Much like the earliest tetrapods, elephants were thought to have crawled out of the swamp. It was this transition to land, and the opening of migratory routes through Asia and into North America, that transformed them into more familiar forms. This was represented by an illustration in a 1907 Century magazine article about the wonderous fossils of the Fayum deposits.

This was a much simplified version of what was then thought to represent the straight-line evolution of elephants. There were a lot of fossils between Palaeomastodon and Mammuthus. Even then, though, the image many paleontologists wanted to invoke was a straight line. Genera like Mammut, Deinotherium, and Platybelodon (named in 1928) were pushed off to the side as failed experiments in elephant evolution. Evolutionary diagrams of elephant evolution in technical journals did show branching patterns, that is true, but it was the branch that led to living forms, the "winners in life's race", that were always of the most important. The rest could be relegated to the trash bin of earth's history.