''Ozarcus'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

of symmoriiform from the Carboniferous period of

Arkansas Arkansas ( ) is a landlocked state in the South Central United States. It is bordered by Missouri to the north, Tennessee and Mississippi to the east, Louisiana to the south, and Texas and Oklahoma to the west. Its name is from the O ...

. The type species, ''Ozarcus mapesae'', was named in

2014 File:2014 Events Collage.png, From top left, clockwise: Stocking up supplies and personal protective equipment (PPE) for the Western African Ebola virus epidemic; Citizens examining the ruins after the Chibok schoolgirls kidnapping; Bundles of wat ...

based on

cartilaginous Cartilage is a resilient and smooth type of connective tissue. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck a ...

skulls from the

Serpukhovian The Serpukhovian is in the ICS geologic timescale the uppermost stage or youngest age of the Mississippian, the lower subsystem of the Carboniferous. The Serpukhovian age lasted from Ma to Ma. It is preceded by the Visean and is followed b ...

-age

Fayetteville Formation The Fayetteville Shale is a geologic formation of Mississippian age (354–323 million years ago) composed of tight shale within the Arkoma Basin of Arkansas and Oklahoma. It is named for the city of Fayetteville, Arkansas, and requires hydraulic ...

. The genus is named after the

Ozark Mountains The Ozarks, also known as the Ozark Mountains, Ozark Highlands or Ozark Plateau, is a physiographic region in the U.S. states of Missouri, Arkansas, Oklahoma and the extreme southeastern corner of Kansas. The Ozarks cover a significant port ...

(the region of discovery) while the species was named after its discoverer, G. K. Mapes. The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of sever ...

fossil,

AMNH The American Museum of Natural History (abbreviated as AMNH) is a natural history museum on the Upper West Side of Manhattan in New York City. In Theodore Roosevelt Park, across the street from Central Park, the museum complex comprises 26 i ...

FF20544 (formerly labelled as OUZC 5300), was a warped yet three-dimensionally-preserved skull with gill baskets. Three additional skulls referrable to ''Ozarcus'' are stored at the AMNH. A partial braincase ( FMNH PF 13242) from the same site, previously been referred to '' Cobelodus'' and described in detail in 2007, was referred to ''Ozarcus'' in 2017. ''Ozarcus'' has branchial arches (bones of the gill basket) with unexpected similarities to osteichthyans (bony fish) rather than chondrichthyans (cartilaginous fish). Like other jawed fish, there are five pairs of branchial arches, not counting the larger

hyoid The hyoid bone (lingual bone or tongue-bone) () is a horseshoe-shaped bone situated in the anterior midline of the neck between the chin and the thyroid cartilage. At rest, it lies between the base of the mandible and the third cervical vertebra. ...

arch which lies in front of the gills and behind the jaws. Each branchial arch starts with basibranchial and hypobranchial bones along the lower midline of the throat, linking upwards tobackwards-leaning ceratobranchials, then forwards-leaning epibranchials, and finally blocky pharyngobranchials. Unlike modern chondrichthyans, the first four branchial arches have two pairs of pharyngobranchials which bend forwards to form a solid roof to the gill cavity, conditions akin to the two sets (infra- and supra-pharyngobranchials) of osteichthyans. In addition, the hypobranchials flanking the lower midline also project forwards, in contrast to living sharks. The initial description of ''Ozarcus'' tentatively placed it as a member 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 ...

, based on its small teeth similar to ''

Falcatus ''Falcatus'' is an extinct genus of falcatid chondrichthyan which lived during the early Carboniferous Period in Bear Gulch bay in what is now Montana. Description This fish was quite small, only getting to around 25–30 cm or 10-12 i ...

'' and ''

Damocles Damocles is a character who appears in an (likely apocryphal) anecdote commonly referred to as "the sword of Damocles", an allusion to the imminent and ever-present peril faced by those in positions of power. Damocles was a courtier in the cou ...

''. Falcatids were a type of symmoriiform,

shark Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachi ...

-like fish which were probably distant relatives of modern

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 ...

. In contrast, later papers placed ''Ozarcus'' (represented by specimen FMNH PF 13242) as the sister taxon to ''

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 ...

'' or close to the base of Symmoriiformes, far away from the falcatid ''Damocles''.

References

{{Taxonbar, from1=Q21445942, from2=Q22109539 Symmoriiformes Carboniferous fish of North America Fossil taxa described in 2014