|Period||Middle Jurassic period|
|Location||England, France, Germany, Chile|
|Length||under debate, about 16 meters|
Leedsichthys problematicus was an 54 foot filter-feeding fish from the Jurassic time period. This is the largest fish that ever lived and its closest modern-day relative is the bowfin. It shows signs of parallel evolution with the baleen whales and modern filter-feeding sharks (especially the basking shark). It was probably a passive feeder, swimming with its mouth open and on occassion closing the jaws to squeeze the water out and swallow the plankton.
Like the other plankton-eating animals, Leedsichthys was likely a migratory, nomadic creature, travelling around the world in search of plankton. Its giant sized protected it from smaller predators, like Hybodus, a prehistoric shark, and Metriorhynchus, an aquatic crocodilian, but the bigger carnivores, the pliosaurs, were probably a regular threat to this giant.
The first remains of Leedsichthys were identified in the nineteenth century. Especially important were the finds by the British collector Alfred Nicholson Leeds, after whom the genus was named "Leeds' fish" in 1889.