''Dinichthys'' (from , 'terrible' and 'fish') is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

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 "unispe ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of large marine

arthrodire Arthrodira (Greek for "jointed neck") is an Order (biology), 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 penetratin ...

placoderm Placoderms (from Ancient Greek πλάξ 'plax'', ''plakos'''Plate (animal anatomy), plate' and δέρμα 'derma'''skin') are vertebrate animals of the class (biology), class Placodermi, an extinct group of prehistoric fish known from Pal ...

from the

Late Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era during the Phanerozoic eon, spanning 60.3 million years from the end of the preceding Silurian period at million years ago ( Ma), to the beginning of the succeeding ...

(

Famennian The Famennian is the later of two faunal stages in the Late Devonian epoch. The most recent estimate for its duration is that it lasted from around 371.1 to 359.3 million years ago. An earlier 2012 estimate, still used by the International Commis ...

stage) measuring around long. Fossils were recovered from the Ohio Shale Formation along the Olentangy River in

Delaware County, Ohio Delaware County is a county located in the central portion of the U.S. state of Ohio. As of the 2020 census, the population was 214,124. Its county seat and largest city is Delaware. The county was formed in 1808 from Franklin County, Ohio. Bo ...

Classification History

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

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

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

Dunkleosteus ''Dunkleosteus'' is an extinct genus of large arthrodira, arthrodire ("jointed-neck") fish that existed during the Late Devonian period, about 382–358 million years ago. It was a pelagic fish inhabiting open waters, and one of the first verteb ...

'', ''

Eastmanosteus ''Eastmanosteus'' ("Eastman's bone") is a fossil genus of Dunkleosteidae, dunkleosteid placoderms. It was closely related to the giant ''Dunkleosteus'', but differed from that genus in size, in possessing a distinctive tuberculated bone ornament, ...

'', and '' Titanichthys''. Notably, the

type species In International_Code_of_Zoological_Nomenclature, 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 spe ...

of ''Dunkleosteus'' was originally described as ''Dinichthys terrelli'' by Newberry in 1873, and was later separated into ''Dunkleosteus'' by

Jean-Pierre Lehman Jean-Pierre Lehman (10 August 1914 – 26 February 1981) was a French paleontologist who specialized on tetrapods and actinopterygians. He followed early ideas comparative anatomy to study evolution through cladistic ideas and making use of bio ...

in 1956. ''Dunkleosteus'' was still thought to be closely related to ''Dinichthys'', and they were grouped together in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Dinichthyidae. However, in the 2010 Carr & Hlavin

phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

study, ''Dunkleosteus'' and ''Dinichthys'' were found to belong to two separate

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

s. Carr & Hlavin resurrected the family

Dunkleosteidae Dunkleosteidae is an extinct family (biology), 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 Dunkleo ...

and placed ''Dunkleosteus'', ''

'', 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 "unispe ...

, containing only the

, ''D. herzeri''.

Phylogeny

''Dinichthys'' is a member of the

Aspinothoracidi, which belongs to the clade Pachyosteomorphi, one of the two major clades within Eubrachythoraci. The

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

below shows the

phylogeny A phylogenetic tree or phylogeny is a graphical representation which shows the evolutionary history between a set of species or Taxon, taxa during a specific time.Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, M ...

of ''Dinichthys'':

References

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