Hyaenodon horridus Skull - 11 inches

Hyaenodon is an extinct carnivorous mammal known as a creodont. H. horridus was the largest of all the Hyaenodons weighing up to 130 lb. 

Location: Custer County, South Dakota (Brule Formation, White River Badlands Group)

Age:  Oligocene (30 - 34 million years old).

This skull measures 11 inches / 28 cm long, 6 inches / 16 cm wide, 5.5 inches / 14 cm heigh. Weighs 2350 g / 5 lb 2 oz.