One Christmas my brother presented me with a fossilised fish, labelled as Diplomystus from the Green River Formation in Wyoming, USA. The fossil was correct in that it belonged to the Clupeidae family, although further research has led me to believe it is in actual fact Knightia eocaena. Both are extinct family members of the sardine and herring family.
HABITAT AND DISTRIBUTION
Knightia eocaena fossils have been found in freshwater lakes along the Green River Formation in southern Wyoming, USA.
Similar to today's Clupea herrings, Knightia eocaena was once believed to belong to the same genus. Growing up to 25cm (10 inches) in length, this species was the largest of the 6 species that made up the extinct genus Knightia. One of the main reasons I questioned the original identification was the lack of length to the anal fin (in Diplomystus it runs from the middle of the belly to the tail fin, this specimens anal fin starts around three quarters of the way along the belly). Also the tail fin is very pointed and narrow, whereas it appears much longer and more rounded in the Diplomystus specimens. The Diplomystus tend to have a larger bumped 'forehead' than Knightia.This species had scutes (bony plates) both on its dorsal and its ventral side. Its teeth were conical in shape and the scales were heavy. Its main diet was most probably plankton and algae, but it may have eaten small fish and insects too.
DIET, BEHAVIOUR AND REPRODUCTION
Knightia eocaena moved in schools, and that has led to there being an abundance of fossils available today.
OTHER NOTABLE FACTS
Knightia species were preyed upon by other larger fish (such as Diplomystus and Mioplosus) and the extinct snake Boavus idelmani. Living during the Eocene Epoch (55.8 - 33.8 million years ago) it is still unclear as to their demise.
Knightia eocaena is listed by the IUCN as Extinct, no members of its genus are alive today.