Leedsichthys problematicus (in the background) being harrassed by a plesiosaur; painting by Dmitry Bogdanov

Leedsichthys (Leedsichthys problematicus) was the largest known bony fish.  It lived during the middle Jurassic (155 million years ago), feeding on algae, plankton, and small shrimp & fish—much like a modern whale shark or baleen whale.  Leedsichthys had over 40,000 teeth with which to skim its meal from the water.  Although most of these huge fish were around 12 meters (approximately 40 feet) or smaller in length, many scientists believe that Leedsichthys was capable of growing much larger.  Fragmentary specimens suggest they attained lengths greater than 17 meters (about 55 feet) and even larger individuals might be found.

Painting by Dmitry Bogdanov

Leedsichthys is named after Alfred Nicholson Leeds, who discovered its fossilized remains in 1886 in England.  He had so much trouble piecing the bones together that he gave the fish the species name of “problematicus”.  Leedsicthys was most likely a global species with a presence in all of the open oceans of the Jurassic world.  It is unclear why the species went extinct, but paleontologists have speculated that it was out-competed by the teleosts–the modern bony fish–which lay vastly more eggs than pachycormids like Leedsichthys.

The world 155 million years ago. No Atlantic Ocean!