As this group scampers toward the river, we can see that they have a peculiar crouching gait—their forelegs are so much shorter than their hind legs that they seem to be running continuously downhill. They are dainty little animals with small, delicate heads and short, slender limbs. They can bound swiftly away if danger threatens, but they’d rather hide in the thick brush. A few of the females have fawns with them, tiny things less than 10 centimeters (4 inches) tall. Look at them all scatter! The shadow of a hawk has passed over the group, and in their fright they’ve dived for some nearby willows. Young _Nanotragulus_ either learn to duck down at the sight of a passing shadow or they don’t get a chance to learn at all. This time they all got away, and the hawk will have to look elsewhere for a meal.
Buteos or buzzard hawks are common along the Niobrara in the Early Miocene, sailing on the warm updrafts on broad, short wings that let them ride the lightest airs. They swoop down on the mice and pocket gophers, young rabbits and beavers, baby “deer” and sometimes careless birds that live on this savanna. All manner of meat-eaters depend on the small animals for food, and the little _Nanotragulus_ are most vulnerable as they move through the canopy of grass.
There don’t seem to be any other herds moving into view just now; but while we’re on the subject of birds, over there in that patch of short grass is a bird rarely seen in North America anymore. It’s a guan, a ground-living bird related to the grouse and sagehens. It must be far from home this morning; most of its time is spent in the thick brush farther back from the river. A heavy body and long neck and tail make this animal easy to identify.
Let’s look at some of the individuals and small groups that are moving or resting within view. The camels with the very slender legs and long necks are called _Oxydactylus_ (“sharp finger”). They are browsing on the willows where the herd of Nanotragulus ran to hide. _Oxydactylus_ is an important camel, standing about at the midpoint in the evolution of this North American family of mammals. The camels will remain stay-at-homes in the continent of their origin until they spread into Eurasia and South America at the beginning of the Pleistocene Epoch, some 17.5 million years after the rhinos died out at Agate. There are many species of _Oxydactylus_; the one we are looking at stands about 1.2 meters (4 feet) high at the shoulder. Notice that they don’t have humps on their backs; in this lush land there is no need to store fat against a time of possible starvation.