Symmoriiformes is an extinct order of holocephalians. Originally named Symmoriida by Zangerl (1981), it has subsequently been known by several other names. Lund (1986) synonymized the group with Cladodontida, while Maisey (2008) corrected the name to Symmoriiformes in order to prevent it from being mistaken for a family. The symmoriiform fossils record appear at the beginning of the Carboniferous. Most of them died out at the start of the

Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last ...

, but ''

Dwykaselachus ''Dwykaselachus'' (pronounced dwike-a-selak-us) is an extinct genus of symmoriiform, a cartilaginous fish that lived in what is now South Africa during the Permian period around 280 million years ago. It was first discovered in the 1980s, in a ...

'' is known from the

Artinskian In the geologic timescale, the Artinskian is an age or stage of the Permian. It is a subdivision of the Cisuralian Epoch or Series. The Artinskian likely lasted between and million years ago (Ma) according to the most recent revision of th ...

Kungurian In the geologic timescale, the Kungurian is an age or stage of the Permian. It is the latest or upper of four subdivisions of the Cisuralian Epoch or Series. The Kungurian lasted between and million years ago (Ma). It was preceded by the Ar ...

of South Africa. Teeth described from the

Valanginian In the geologic timescale, the Valanginian is an age or stage of the Early or Lower Cretaceous. It spans between 139.8 ± 3.0 Ma and 132.9 ± 2.0 Ma (million years ago). The Valanginian Stage succeeds the Berriasian Stage of the Lower Cretace ...

of France and Austria indicate that members of the family

Falcatidae Falcatidae is a family of Paleozoic holocephalians. Members of this family include ''Falcatus'', a small fish from the Bear Gulch Limestone of Montana. The family first appeared around the start of the Carboniferous, and there is some evidence ...

might have survived until the Early Cretaceous; however, these teeth were also argued to be more likely neoselachian teeth.

Fossil distribution

Fossil evidence of Symmoriida have been found at Bear Gulch,

Fergus County, Montana Fergus County is a county in the U.S. state of Montana. As of the 2020 census, the population was 11,446. Its county seat is Lewistown. The county was founded in 1885 and named for James Fergus, a Montana politician who was instrumental in cr ...

, Bethel Quarry,

Pike County, Indiana Pike County is a county in the southwest portion of the U.S. state of Indiana. As of the 2010 United States Census, the population was 12,845. The county seat is Petersburg. It contains the geographic point representing median center of US popu ...

, Kinshozan quarry, Alaska, Gifu Prefecture, Japan, Bashkortostan,

Russian Federation Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-eig ...

and possibly also

France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of overseas regions and territories in the Americas and the Atlantic, Pacific and Indian Oceans. Its metropolitan area ...

Classification

The symmoriiformes have been assigned to Cladoselachii by Goto et al. (1988), to Elasmobranchii by Williams (1998), and to

Chondrichthyes Chondrichthyes (; ) is a class that contains the cartilaginous fishes that have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or ''bony fishes'', which have skeletons primarily composed of bone tissue. ...

by Sepkoski in 2002 and by Maisey in 2008. The uncrushed braincase of ''

'' indicates that symmoriiforms are members of

Holocephali Holocephali ("complete heads"), sometimes given the term Euchondrocephali, is a subclass of cartilaginous fish in the class Chondrichthyes. The earliest fossils are of teeth and come from the Devonian period. Little is known about these primitiv ...

, as much of the internal anatomy, including the otic labyrinth and brain space configuration are similar to those of

chimaeras Chimaeras are cartilaginous fish in the order Chimaeriformes , known informally as ghost sharks, rat fish, spookfish, or rabbit fish; the last three names are not to be confused with rattails, Opisthoproctidae, or Siganidae, respectively. At o ...

Gallery

References

*http://palaeo.gly.bris.ac.uk/benton/vertclass.html {{Taxonbar, from=Q139057 Symmoriiformes Prehistoric cartilaginous fish orders