This Knightia mortality plate is from the Green River Formation, Fossil Lake, WY and containes many Knightia fossil fish from 2 1/4" to more than 4" long. These groupings of multiple fish are referred to as "mortality layers" and are believed to have been caused by large amounts of ash fall-out after volcanic eruptions. The Knightia, members of the family that includes the modern herring, are brown on a creamy limestone. This large plate is suitable for a mantle piece or large wall. Size is approximate 15 1/2" x 12" x 3/4", with a weight of just under six pounds, listed retail for $400.00. These fossils are known to be from 40-60 million years old (Eocene Age) and are in excellent state of preservation. It is generally acknowledged that the finest fossil fish come from Fossil Lake. These fossils have been cleaned and prepared to offer a quality fossil for your enjoyment, study and preservation.