''Holdenius'' 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 ...

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 ...

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 ...

fish which lived during the Late

Devonian period 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 C ...

Description

''Holdenius'' was a large arthrodire, reaching lengths of around . This placoderm is known only from isolated jaw bones, and little is known about it except that it is relatively morphologically similar to its more famous relative ''

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 ...

'', with which it shared a spatial and temporal range. ''Holdenius'' was a

piscivorous A piscivore () is a carnivorous animal that primarily eats fish. Fish were the diet of early tetrapod evolution (via water-bound amphibians during the Devonian period); insectivory came next; then in time, the more terrestrially adapted rept ...

animal that used its sharp shearing gnathal plates to seize and cleave its prey into manageable pieces. One articulated specimen of this placoderm from the Upper Devonian

Cleveland Shale The Cleveland Shale, also referred to as the Cleveland Member of the Ohio Shale, is a Late Devonian (Famennian) shale Member (geology), geologic member in the eastern United States. Identification and name The Cleveland Shale was identified in ...

was preserved adjacent to the remains of its prey; a '' Ctenacanth''

chondrichthyan Chondrichthyes (; ) is a class (biology), class of jawed fish that contains the cartilaginous fish or chondrichthyans, which all have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or ''bony fish'', which ...

, which had been bitten in half. Considering its prey was over half its size, it can be inferred that ''Holdenius'' was an exceptionally aggressive

nektonic Nekton or necton (from the ) is any aquatic organism that can actively and persistently propel itself through a water column (i.e. swimming) without touching the bottom. Nektons generally have powerful tails and appendages (e.g. fins, pleopods ...

predator. An anterior

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage The fus ...

spine from the ctenacanth was found lodged in the

palate The palate () is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but in most other tetrapods, the oral and nasal cavities are not truly sep ...

and extending into the braincase of the ''Holdenius'', likely killing it instantly.Brett, Carlton & Walker, Sally. (2002). Predators and Predation in Paleozoic Marine Environments. Paleontological Society Papers. 8. 10.1017/S1089332600001078. ''Holdenius'' is a

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. Previously classified as belonging to 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 ...

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 ...

, it is now considered to be a member of

Aspinothoracidi Aspinothoracidi is a clade of placoderms, extinct armored fish most diverse during the Devonian. The gigantic apex predator ''Dinichthys'', is the best-known member of this group. Many other genera, such as the infamous ''Dunkleosteus'', were pre ...

, the

sister A sister is a woman or a girl who shares parents or a parent with another individual; a female sibling. The male counterpart is a brother. Although the term typically refers to a familial relationship, it is sometimes used endearingly to ref ...

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 ...

Dunkleosteoidea Dunkleosteoidea is an extinct superfamily of arthrodire placoderms that lived during the Devonian period. The gigantic apex predator ''Dunkleosteus terrelli'' is the best known member of this group. Phylogeny Eubrachythoraci is divided into the ...

References

{{Taxonbar, from=Q5879588 Arthrodires Arthrodire genera Placoderms of North America Late Devonian animals