During the 1930s and early 1940s large collections of fossils were removed from excavations in Nebraska by workers funded by the Works Progress Administration (WPA) of the United States government. These excavations, under the supervision of UNSM paleontologists, produced large numbers of plaster-jacketed specimens removed from sites sampling ancient river, stream and waterhole deposits of Miocene age (~24 million to 5 million years). Despite continuous preparation of this material in our laboratory, over 3000 jackets remained to be opened and evaluated in 2006, prior to incorporation and conservation in the UNSM collections. Of these, ~40% are from the early Miocene Hemingford Quarries of western Nebraska. The Hemingford mammal fauna fills an important temporal gap in the Miocene biochronology of North America, nowhere so well represented as at these sites. With this situation in mind, a proposal presented to the National Science Foundation in 2005 resulted in an award to the Division of Vertebrate Paleontology that included funding for the preparation of a portion of the backlog of plaster-jacketed material from the WPA excavations. During 2006-2008 these jackets yielded hundreds of bones of Miocene camels, horses, rhinoceroses, and carnivores to the UNSM collections.
Because specimens were excavated by WPA field workers who were not experienced in the identification of fossil mammals, it was anticipated that particularly unique and important material might be discovered during preparation of unopened jackets from the various Hemingford Quarries. This proved to be the case, and among the most interesting finds were bones of a rare large Miocene wolf-like carnivore belonging to the extinct family Amphicyonidae, better known as beardogs. First recognized in 1910 from a few foot bones and a fragment of the jaw, most of the skeleton of this carnivore, formally named Borocyon, remained poorly known until the preparation of the Hemingford jackets began to produce limb and foot bones, skulls, jaws, and teeth. Gradually much of the skeleton came to light over two years, revealing a large agile predator from the early Miocene, an efficient, broad-skulled runner with massive jaws able to slice meat and grind bone, much like living wolves, but with some anatomical parallels to large cats. Reconstruction of this animal suggests that it was the dominant predator of its time yet became extinct about 17-18 million years ago with no descendants. Ongoing preparation of the remaining backlog of field jackets promises additional discoveries that enrich our knowledge of the Cenozoic fauna of Nebraska and the surrounding region.