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Diggin' For Dinosaurs - John Day Fossil Beds
John Day Fossil Beds National Monument, Oregon
When dinosaurs roamed North America, much of what is now John Day Fossil Beds lay under the ocean. Eventually, the land here began to lift. Massive, mile-thick lava flows blanketed the region. Eruptions of ash and basalt obliterated the seascape but put ground beneath the feet of the dinosaurs- successors: the mammals.
Geologic forces have since lifted and sliced through these rock layers, exposing one of the longest and most complete fossil records of its kind. Dating from 54 million to 6 million years ago, the fossil beds capture the evolution of mammals throughout most of the Tertiary, the geological period between the extinction of the dinosaurs and the Ice Ages.
The oldest layers preserve in great detail the plants and animals that lived in subtropical forests. Strange-looking, rhinoceros-like brontotheres dominated the landscape, along with big predatory Patriofelis and the scavenger Hemipsalodon. These layers also contain the Clarno Nutbeds, among the finest plant fossils on Earth - seeds and fruit so complete that hundreds of species have been identified. Fossil bananas, palms, and kiwis suggest an ancient climate like Southeast Asia's today.
Younger layers document a slowly drying climate, an increasing variety of habitats, and an explosion of plant and animal types. More than 100 species of mammals have been found in layers dating to the early Miocene, when mammalian diversity peaked in North America. Among the great variety of fossils are saber-toothed cats, "mouse-deer," giant pigs, and distant ancestors of rhinoceroses, camels, and horses. Still younger rocks record open savannas on lush volcanic soils and the invasion of such large Asian mammals as elephants and bear-dogs. Then, toward the end of the Tertiary, familiar herds of grazing mammals replaced the browsers in the cool, dry rain shadow of the young Cascade Mountains.
Today, John Day Fossil Beds National Monument is at the scientific heart of this fossil-rich region in eastern Oregon. Palaeontologists here actively piece together past ecosystems to learn more about changing climate and how species adapted and evolved. Besides being one of the best fossil-viewing areas in the Northwest, the monument offers a spectacularly rugged landscape of deeply incised canyons just a few hours- drive from Portland. Here in the Basin and Range country of central Oregon, the John Day River cuts through the Columbia Plateau, creating a beautiful setting for fly-fishing and river rafting.
The past is easy to read in the John Day basin, and the monument has developed several places and activities to enliven the story. The visitor center at Sheep Rock displays a variety of mammal and nut fossils plus exhibits about the collectors themselves, from pioneers to contemporary scientists. The showpiece here is a big rhinoceros, Dicerantherium annectens. Nearby, the Island of Time Interpretive Trail invites visitors to experience the fossil beds firsthand and helps train one's skills as a bone hunter. For those with time to explore the three widely spaced units that comprise the monument, a logbook prepared by the Society of Vertebrate Palaeontology makes an excellent driving guide to the deep history embedded in the basin's colorful rock layers.
For families and groups interested in a deeper look, the Hancock Field Station, operated in the monument by the Oregon Museum of Science and Industry in Portland, offers weekend programs in palaeontology and natural history. Guests stay in rustic cabins and take classes in fossil collecting and stargazing.