Dinohyus
Look down toward the river, and we may see an exception. That two-meter (six-foot) high “pig” walking away from the river, covered with mud, is heading right toward the Moropus. His name is Dinohyus (“terrible pig”), and he’s just as short-tempered and stupid as Moropus. He looks like a giant peccary, but his size and over-large head give him away as an entelodont (“complete tooth”). These are pig-like animals, usually of large size, that aren’t related to the domestic pigs at all. Dinohyus’ skull is nearly one meter (three feet) long, and those tusks are as thick as a man’s wrist. Though we missed seeing him earlier, he must have been wallowing in the mud under the overhanging willows. Now he’s heading away from the river in search of lunch. He’s not very choosy about what he eats; it might be succulent leaves or fruits, or even the carcass of a dead animal. Dinohyus is an omnivore, eating almost anything that has nourishment.
Right now it looks as though he’s on a collision course with the Moropus. He’s seen the larger animal, has stopped in his tracks, and is pawing the ground with his front feet. Up goes his head—and listen to that roar! He’s getting a good temper worked up. Off he goes at a full gallop, right toward the Moropus. It’s hard to believe that an animal as big as that pig could charge so fast. And look at the Moropus! He’s finally realized in his dim way that he’s about to be attacked. Up he goes on his hind legs, holding his front legs out ready for a downward blow with all eight claws. But suddenly Dinohyus shifts his course just slightly, lets out another loud bellow as he avoids the Moropus, and thunders off toward the open prairie.
Dinohyus has a smaller relative around here somewhere, a little fellow just over one meter (three feet) high, called Entelodon. His head is long and low and has flaring cheekbones and bumps along the underside of the jaw like his larger cousin’s. Another pig that lives along the Niobrara is Desmathyus (“bond [filling a gap] pig”), a true North American pig or peccary. Its appearance probably wouldn’t surprise anyone; it looks very much like the peccaries that live in the American Southwest today. Its distant cousin, the domestic pig, was domesticated in the Old World from a European species of wild hog, and it was spread throughout the world by European colonists. In America, peccary evolution has run a long and conservative path. This group has changed relatively little in the 35 million years since it first appeared in the Late Eocene.
Syndyoceras
Now for another weird and wonderful beast! Trotting daintily out of a thicket on our left is a herd of something you might think were deer or pronghorn. But if you look closely you’ll see that they have two pairs of curving, unbranched horns on their heads, not the single pair of prongs you’d expect on a pronghorn. These are Syndyoceras (“together horn”), members of a family of mammals found only in North America and now extinct. Even on the Early Miocene day we’re visiting, they are scarce, moving only in small herds. The rear pair of horns is not remarkable, but the front ones, which rise from a large bump near the nose, curl up and away from each other, ending in blunt tips.
The first member of this family was Protoceras, which lived in the hills and mountains of western South Dakota during the Late Oligocene, just a few million years before the day we are visiting at Agate. Paleontologists have found battered scraps of its skeletons in the White River Badlands where perhaps they were washed by heavy spring rains running off the hills to the west. Protoceras had six bony bumps on its head that presumably bore short horns; one pair was over the nose, another was over the eyes, and a third was near the back of the skull. Probably it was the direct ancestor of Syndyoceras.
If Syndyoceras fails somehow to qualify as grotesque, let’s jump a few million years into the “future” and look at his Late Miocene descendant, Synthetoceras (“combined horn”). Here was an animal on a par with unicorns and cyclopses. Like Syndyoceras he had two tall horns at the back of his head; but something had happened to the curved ones on his nose. They had, during several million years of evolution, grown together into a single shaft and then spread out again to the sides and up. What a pity there were no little boys then, for here we have the world’s first and only self-propelled slingshot! Tie a rubber band to the tips of his nose horns, fill your pocket with pebbles, and saddle up.
You may be wondering by now about the smaller animals—the rodents and small carnivores. We have not seen any of them so far. Most carnivores work at night, but there should be a few about. Down by the river is a pair of Oligobunis (“little cusp”) hunting near the water’s edge. They look something like modern badgers but are really more closely related to the weasels. If you look just to the right of the herd of Stenomylus we were following earlier you might be able to catch a glimpse of a stalking cat about the size of a mountain lion. It’s probably either an advanced Nimravus (“ancestral hunter”) or an early Pseudaelurus (“false cat”), but we’ll have to get a closer look before we can be sure. Whichever it is, it’s on the main line of cat evolution and will eventually end up in our familiar Felis and the other living cats. There should also be some sabretooth cats lurking about; they are found in nearby deposits of the same age, though not at Agate itself.