Gyrodus is the only member of the pycnodont family Gyrodontidae, which can be distinguished by certain traits such as a depressed pit in the occlusal surface of the teeth, and four dentary teeth. The sister group to this family is thought to be the
hypercarnivorous Serrasalmimidae, of which one genus (
Polygyrodus) was previously placed in the Gyrodontidae. The following species are known: In the past, many other species were known, but almost all were synonymized with
G. circularis and
G. hexagonus. The earliest definite record of
Gyrodus is from the
Middle Jurassic (
Bajocian) of Scotland, which was initially assigned to the species
G. goweri, but is likely too fragmentary for a species description. They become much more common during the Late Jurassic, and fossils of
Gyrodus are common throughout Europe, including France (including the
Cerin Lagerstatte), Germany, Switzerland (
Reuchenette Formation), Italy, and Spain. From the Americas, it is known from the Late Jurassic of Chile and the
Kimmeridgian of Mexico. In Asia, it is known from the Tithonian of Japan and Siberia. During the Early Cretaceous, indeterminate
Gyrodus remains are known from the
Barremian &
Hauterivian of Germany, with the final known record of
Gyrodus being remains assigned to the species "
G. minor" from the
Aptian of England. == Palaeobiology ==