Badlands National Park - Preservation in Stone

Among the most interesting erosion-resistant rocks in the Badlands are those known as concretions. Like pearls within oysters, they form within sedimentary layers when minerals adhere to foreign bodies. Often the foreign bodies are fossils: some large, some very small. In one study of 189 Badlands anthills, all but one contained tiny fossils that had been excavated by harvester ants from their deep burrows. These included lizard and fish parts, mammal teeth, and seeds, mostly from hackberry trees (they look like white BB's).

Where erosion has cut all the way down to bedrock, there appear fossils of animals that lived in the shallow ocean of 65 to 80 million years ago, including many marine turtles. One fossil turtle 12 feet long was found in the Badlands. The shells of these saltwater giants and of smaller, more numerous, and much more recent land turtles are the most noticeable animal fossils, though their shards are sometimes mistaken for broken pots. The shells have lasted millions of years but quickly disintegrate when finally exposed to the air.

The Badlands yield a wondrous number and variety of fossils from Oligocene times; they simply fall out of the fast-eroding landscape. None are larger than titanothere bones. Bigger than the average rhinoceros, this titanic creature had a pair of horns projecting from the end of its huge nose in a blunt, V-shaped prong. The horn was presumably for defense, but size alone must have protected healthy titanotheres, even from such fearsome predators as saber-toothed cats and the wolf-like Hyaenodon horridus.

The first titanotheres, about the size of a young calf, lived 50 million years ago. Gradually, bigger versions evolved, browsing on plentiful leaves and new-growth twigs. At last, their heads alone were three feet long and contained molars four inches square. But when the lush forests of the early Oligocene were replaced by grassland, titanotheres died out, leaving no descendants. Coincidentally, three kinds of rhinoceros also roamed the area. These were unrelated to the titanotheres, although one kind did sport side-by-side nose horns. All Badlands rhinos, of course, are long extinct.

The commonest Oligocene mammals were the 22 species of oreodonts that ranged across the northern Great Plains. Their name refers to teeth shaped like mountains, but some of their teeth resembled those of cows, and their canines were short tusks. Their bodies varied in length from two to five feet, and all looked rather like pigs. (Speculating that they might have chewed cuds, scientists once called them ruminating pigs.) Each had an ecological niche in which it thrived: some were largely aquatic; some may have climbed trees; one even had claws. Adaptable as they were, oreodonts also died out without descendants.

Another piglike animal, the entelodont, had wide, protruding cheekbones, a humped back, a small brain, and an assortment of teeth designed to eat just about anything. Up to 6 feet tall and 10 feet long, it is also called a giant pig, although it left no descendants when it went the way of the titanothere. True pigs originated in the Old World.

The protoceras, the name means "early horns", was a sheep-sized beast whose lithe body was built for running and jumping. The male, with three pairs of knobby horns protruding from its head and face, may well have been the oddest-looking mammal of the Oligocene Badlands.

Horses, but not the modern version, also roamed the landscape. The two types that have been identified in Badlands National Park, Mesohippus and Miohippus, were about the size of collie dogs. They had three toes on each foot, the middle toe distinctly larger than the other two, forecasting the hoof of the modern horse.

Before 1850, petrified bones of these and many other now-extinct Oligocene mammals littered the landscape. Indians invented a mythical thunderhorse to account for the largest of them. But in the mid-19th century scientists descended, hauling petrified bones away by wagonloads for museums all over the world. Today it is rare to find a big fossil bone in the Badlands.

Much of this collecting was done on the run, for fear of hostile Indians. One collector, Ferdinand V. Hayden, was captured with the pockets of his frock coat full of fossils. The Indians assumed that anyone dressed so oddly who ran about picking up useless rocks had to be crazy. With their customary respect for the insane, they let him go to pursue a brilliant scientific career.