''Dinichthys'' (from el, δεινός , 'terrible' and el, ἰχθύς 'fish') is an extinct

monospecific In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...

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 giant, marine

arthrodire Arthrodira (Greek for "jointed neck") is an order of extinct armored, jawed fishes of the class Placodermi that flourished in the Devonian period before their sudden extinction, surviving for about 50 million years and penetrating most marine eco ...

placoderm from the Late Devonian (

Famennian The Famennian is the latter of two faunal stages in the Late Devonian Epoch. The most recent estimate for its duration estimates that it lasted from around 371.1 million years ago to 359.3 million years ago. An earlier 2012 estimate, still used b ...

stage), comparable in size, shape, and ecological role to the better-known ''

Dunkleosteus ''Dunkleosteus'' is an extinct genus of large armored, jawed fishes that existed during the Late Devonian period, about 382–358 million years ago. It consists of ten species, some of which are among the largest placoderms to have ever lived: ...

''. Fossils were recovered from the Ohio Shale Formation along the

Olentangy River The Olentangy River is a tributary of the Scioto River in Ohio, United States. History It was originally called ''keenhongsheconsepung'', a Delaware word literally translated as "sharp tool river", based on the shale found along its shores ...

Delaware County, Ohio Delaware County is a county located in the central portion of the U.S. state of Ohio. It is a frequent placeholder on the List of highest-income counties in the United States. As of the 2020 census, the population was 214,124. Its county seat ...

Classification History

''Dinichthys'' was originally described in 1868 by John Newberry on the basis of an incomplete skull roof and mandibles (

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 ...

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 ...

81). Subsequently, many unrelated large arthrodires were originally classified together within this genus, including species now assigned to ''

'', '' Eastmanosteus'', and ''

Titanichthys ''Titanichthys'' is an extinct genus of giant, aberrant marine placoderm from shallow seas of the Late Devonian of Morocco, Eastern North America, and possibly Europe. Many of the species approached ''Dunkleosteus'' in size and build. Unlike its ...

''. Notably, the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specime ...

of ''Dunkleosteus'' was originally described as ''Dinichthys terrelli'' by Newberry in 1873, and was later separated into ''Dunkleosteus'' by Jean-Pierre Lehman in 1956. ''Dunkleosteus'' was still thought to be closely related to ''Dinichthys'', and they were grouped together in the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Dinichthyidae. However, in the 2010 Carr & Hlavin

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

study, ''Dunkleosteus'' and ''Dinichthys'' were found to belong to two separate clades. Carr & Hlavin resurrected the family

Dunkleosteidae Dunkleosteidae is an extinct family of arthrodire placoderms that lived during the Devonian period. The gigantic apex predator ''Dunkleosteus terrelli'' is the best known member of this group. Phylogeny While members of Dunkleosteidae were pr ...

and placed ''Dunkleosteus'', '' Eastmanosteus'', and a few other genera from Dinichthyidae within it. Dinichthyidae, in turn, is left a

family and dismissed as a family grouping, and the genus ''Dinichthys'' is now considered a

monotypic genus In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...

, containing only the

, ''D. herzeri''.

Phylogeny

''Dinichthys'' is a member of the clade Aspinothoracidi, which belongs to the clade

Pachyosteomorphi Pachyosteomorphi is an extinct clade of arthrodire placoderms within the Eubrachythoraci (of the suborder Brachythoraci), armored fish most diverse during the Devonian. Most are considered to be pelagic (open ocean) long-distance swimmers, lea ...

, one of the two major clades within

Eubrachythoraci Eubrachythoraci is an extinct clade of arthrodire placoderms within the suborder Brachythoraci, armored fish most diverse during the Devonian. Most are considered to be pelagic (open ocean) long-distance swimmers, leading to their widespread d ...

. The

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...

below shows the

phylogeny A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spe ...

of ''Dinichthys'':

References

Arthrodires Placoderms of North America Arthrodire genera Fossil taxa described in 1868 Paleontology in Ohio Monotypic fish genera {{placoderm-stub