Platysomus is an extinct genus of ray-finned fish that lived in the Carboniferous

Carboniferous

The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...

 and Permian

Permian

The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...

 periods. Fossils have been found worldwide.

Platysomus was about 18 centimetres (7.1 in) long, and shaped similarly to the discus

Discus (fish)

Discus are a genus of three species of cichlid freshwater fishes native to the Amazon River basin. Discus are popular as aquarium fish and their aquaculture in several countries in Asia is a major industry.-Taxonomy:...

 fish, having the same flattened body and alongated dorsal

Dorsal fin

A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...

 and anal fins. Its jaws were placed vertically under the braincase, giving it a wide gape. Platysomus is thought to have fed on plankton

Plankton

Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...

, and lived in both fresh and salt water.