This is a Fossil of a Oreodont Jaw aka Merycoidont sp. The fossil is from the Oligocene Period and found in Northwest Nebraska. 
 Three are three specimens each with a different cost:
A: Measures approx. 36 x 21 mm: thickness is 20 mm: weight is 14 grams ($35)
B: Measures approx. 39 x 24 mm: thickness is 23 mm: weight is 12 grams ($30)
C: Measures approx. 38 x 25 mm: thickness is 25 mm: weight is 15 grams ($25)
 
Oreodont is any member of a diverse group of extinct herbivorous North American artiodactyls. Leptauchenia and Merycoidodon, are often compared to sheep in size and shape. Oligocene Epoch is the third and last major worldwide division of the Paleogene Period (65.5 million to 23 million years ago).