Canobius is an extinct genus of early 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"...

 period of Europe.

Canobius was a small fish, 7 centimetres (2.8 in) in length. Compared with its earlier relatives, it had specialized jaw bones and hyomandibulars which attached the upper jaw to the brain case, meaning that the jaws were hung vertically under the brain case. This allowed Canobius to open its jaws wider and expand its gill

Gill

A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...

 slits further at the same time. In turn this meant that the fish could take in more oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

, making it a more active creature. Canobius is presumed 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...

 which it filtered from the water using its small teeth and gills.