National Geographic : 1981 Jan
bones and teeth in nearby streams and dry washes. Of course, I never dreamed of the treasure of fossil skeletons that lay hidden almost beneath my feet. Three decades later, near sundown on a long day of fossil prospecting, I was walking along the valley rim above a tributary of Verdigre Creek. In cuts and slopes, erosion had laid bare a bed of silvery gray volcanic ash-the fossil-bearing formation-sand wiched between layers of sandstone. Before turning back toward camp, I dropped down to the streambed to explore one more gullied escarpment. Suddenly, high above my head, I saw the skull, gleam ing white against the weathered ash of the ravine wall. Finding the bank too steep to climb, I backtracked to the rim and dropped to a narrow ledge for a closer look. It was a baby rhinoceros skull about a foot long, per fectly preserved, its big teeth glossily mar bled with the dark chemicals of fossilization. Hands trembling with excitement, I gent ly picked and brushed the soft ash away from the skull. To my joy I found it joined to a string of neck vertebrae running back under the hill! In the dark I stumbled back to camp with, for once, a good excuse for being late to supper. "I've never seen anything like it," I told my wife, Jane. "The whole animal could be there." The next day's digging uncovered a bo nanza: Not only was the baby rhinoceros in tact, but the articulated skeletons of three more rhinos, including a full-grown adult, also extended back into the hill. Here was a bone hunter's dream come true. In river deposited layers, such as the sandstone above and below the ash, whole skulls are a rarity and full skeletons almost unheard of. Further testing of the ash bed yielded 12 more skeletons from an area no larger than an average living room. The farmers who held the land, Melvin Colson, who died in 1979, and Carolyn and Glen Osborn, Jr., the present owners, generously let us extend our dig, right to the edge of a cornfield. In June 1978, with support from the National Geographic Society, we brought in a bull dozer and cleared off the surface ash. We staked out with string a pattern of squares three meters on a side to map precisely the position of the fossils we hoped to find. A crew of museum preparators and stu dents worked with me for two field seasons. Like farmers at harvest, we labored from sunup to sundown. Skeletons crowded so close together that we had to crouch uncom fortably to excavate them. Removing them was a challenge. Imagine attempting to lift a sack of thin, cracked wineglasses out of a brier patch without shattering them; that suggests the difficulty of moving brittle, delicate, fossilized bones. To avoid breakage, we first impregnated skulls and bones with a plastic preservative, then "dressed" them in plaster casts. Clus tered in piles, the skeletons looked like par ticipants in a gang tackle in football. A Detailed Record of Prehistoric Life Although our fossil mammals (rhinos, horses, camels, and others) all apparently belong to previously named species, the new skeletons are by far the most complete re mains of these creatures ever unearthed. Rarely found parts such as tongue bones, cartilages, tendons, and tiny bones in the middle ear all survive in exquisite detail and in their correct positions. Such small and fragile parts, like the ten dons of a turkey leg, were only partly calci fied in life, and survived primarily because no action of water, wind, or earth move ment ever shifted them after burial. Frag ments of fossil birds are rare in rocks of this age, so it is likely that totally new forms are represented by skeletons from the ash bed. Volcanic dust again veils the sun on a windy day as a remarkablefossil menagerie is uncovered near the town of Orchard,Nebraska.Excavator Mary Ann Jones, well protected againstglassy grit, brushes the powdery shroudfrom the ribs of a rhinoceros. She will encase them in plasterfor the trip to the University of NebraskaState Museum in Lincoln. Two seasonsof excavations, supported in part by a National GeographicSociety grant, have revealed an unprecedented range of fossils, from complete skeletons of rhinos-thedominant herbivores of this prehistoricsubtropicalsavanna-toturtles and tiny diatoms.