Knightia sp. 5-7cm
Picked at random. Each specimen will vary between 5-7cm on a rock cut slab between 6x9 and 9x13cm.
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.