Fossils: Fossil mammal teeth from the Ash Hollow Formation in Nebraska USA. Approx 10 million years ago to the Miocene Epoch. Approx 20-50mm in length (21). Fossil teeth from the Mastadon species. Approx 4 million years ago, related to the mammoth & modern elephant & native to Eurasia & North America (2). Scarce. See web for photos. (23)