If you look very closely at the thicket just south of us on the hillside you can see several fox-like dogs hunting rodents. This _Nothocyon_ (“false dog”) seems to have filled approximately the fox niche during the Early Miocene. Some coyote and wolf-sized dogs are in the area too. _Daphoenodon_ (“blood-reeking tooth”) is about coyote size. _Temnocyon_ (“cutting [tooth] dog”), is a little larger, probably substituted for the wolf in the local fauna, and is characterized by its heavy head and long, strong jaws. If we could get a close look at its teeth, we would see that they are like those of the Cape Hunting Dog living today in South Africa.
Let’s move away from the river a half-kilometer (0.3 mile) or so and see if we can find something different. That thicket ahead might produce a couple of rabbits. Look, there at the edge of the thicket: a _Nothocyon_ has caught something. It’s a _Meniscomys_ (“crescent mouse”), an early relative of the living mountain beaver _Aplodontia_. Today, a single species of _Aplodontia_, the last of the line, is found only in the mountains of the West Coast. It’s the most primitive living rodent, not related to the Canadian beaver, and sole survivor of a suborder which was the earliest rodent group to evolve. _Meniscomys_ was one of the most prominent members of the group during the Miocene. It had a round furry body, a round head with protruding incisors a bit like a true beaver’s, and no visible tail.
Watch your step. There is the mound of a pocket gopher. It is neither our familiar western gopher _Thomomys_ (“heap mouse”) or the “eastern” pocket gopher of the Great Plains, _Geomys_ (“earth mouse”), but an ancient relative, _Gregorymys_ (“Gregory’s mouse”). It must be pretty successful as a burrowing animal, because we find it all over the western United States in the Early Miocene.
A hundred meters (300 feet) more and we’ll show you the surprise of the day. Here we are in what looks like a prairie dog town. But those aren’t prairie dogs. They’re a little larger, and quite unfamiliar by modern standards. Can’t guess what they are? These are beavers—_Palaeocastor_ (“ancient beaver”) to be exact. Here in the Early Miocene of North America, beavers don’t build dams. In fact they live neither at the water’s edge nor, like muskrats, in the water. They dig deep, spiral burrows in well drained ground. Some of their burrows are 2.5 meters (8 feet) deep, but 2 meters (6.5 feet) is about average. Down and around and around the burrows go, like giant corkscrews, always ending in straight shafts slanting slightly upward so that living chambers will not be flooded by rainwater running down the burrows.