Knightia fossilised fish on a varved limestone matrix collected from the Eocene Green River Formation of Wyoming, USA. Knightia is an extinct genus of bony fish which lived in the fresh water lakes of Asia and North America during the Eocene epoch; they are now recognised as the most excavated fossil fish on earth. They belong to the family Clupeidae which also contain Herring and Sardines and they would have looked morphologically very similar to the former. Around 50 million years ago rapid sedimentation rates within the calm Green River swamps and lakes allowed for the exceptional preservation of fish, plants, animals and insects; resulting in what is known today as a lagerstätte i.e. a sedimentary deposit which exhibits an assemblage of exceptionally preserved fossils. By looking closely at the cut edge of each specimen, fine laminations known as varves can be identified. The laminations represent seasonal changes; the darker coloured, more organic rich sediment represents the growing season while the lighter sediment is indicative of winter. Naturally each fish specimen varies in shape and size but you can expect a specimen which measures between 50 and 90 mm in length. Each fish is preserved on a varved limestone / limey marl matrix which varies from 10 to 14 cm in length, with these matrix slabs being cut as to best preserve the fossil fish and ensure it stays in one whole piece. Each sample will come supplied in a white card tray with an information label, excellent fossil fish, for an excellent price, we have over 50 in stock.