''Plourdosteus'' 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 n ...

of placoderm

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 e ...

which was relatively widespread in

Euramerica Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around (Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the breakup of Pa ...

during the

Givetian The Givetian is one of two faunal stages in the Middle Devonian Period. It lasted from million years ago to million years ago. It was preceded by the Eifelian Stage and followed by the Frasnian Stage. It is named after the town of Givet in ...

Frasnian The Frasnian is one of two faunal stages in the Late Devonian Period. It lasted from million years ago to million years ago. It was preceded by the Givetian Stage and followed by the Famennian Stage. Major reef-building was under way during t ...

ages of the

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, w ...

Etymology

The name ''Plourdosteus'' commemorates the Plourde family at

Miguasha National Park Miguasha Provincial Park (French: ''Parc national de Miguasha'') is a protected area near Carleton-sur-Mer on the Gaspé Peninsula of Quebec in Canada. Created in 1985 by the Government of Quebec, Miguasha was designated a World Heritage Site in ...

Taxonomy

''Plourdosteus'' was previously assigned to 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 ...

Plourdosteidae within the

Coccosteomorphi Coccosteomorphi 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 ...

. However, subsequent studies found the family Plourdosteidae to be

polyphyletic A polyphyletic group is an assemblage of organisms or other evolving elements that is of mixed evolutionary origin. The term is often applied to groups that share similar features known as homoplasies, which are explained as a result of conver ...

and should be dismissed. ''Plourdosteus'' was then proposed to be a member of

Panxiosteidae Panxiosteidae is an extinct family of arthrodire placoderms that lived during the Devonian period. Phylogeny The family Panxiosteidae was erected by Wang in 1979. Members of the family are noted for showing morphologically intermediate traits ...

. 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,

was recognized as the

sister taxon In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

to 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 pre ...

, which together comprised the

superfamily SUPERFAMILY is a database and search platform of structural and functional annotation for all proteins and genomes. It classifies amino acid sequences into known structural domains, especially into SCOP superfamilies. Domains are functional, str ...

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 ...

(one of the three major

clades A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term ...

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 ...

). 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 ''Plourdosteus'' within

is shown in 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 from the 2013 Zhu & Zhu study: However, the subsequent 2016 Zhu ''et al.'' study using a larger morphological dataset recovered

well outside of

, instead within

and then

Coccosteoidea Coccosteoidea is an extinct superfamily of arthrodire placoderms that lived during the Devonian period. Phylogeny Eubrachythoraci is divided into the sister clades Pachyosteomorphi and Coccosteomorphi, the latter of which can be further sub- ...

as the

sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

Coccosteidae Coccosteidae is a family of arthrodire placoderms from the Early to Late Devonian. Fossils appear in various strata in Europe, North America and China. Phylogeny Coccosteidae belongs to the larger clade Coccosteomorphi, which together with i ...

, as shown in the cladogram below:

References

Arthrodires Arthrodire genera Placoderms of North America Placoderms of Europe Fossil taxa described in 1951 Givetian life Frasnian life {{Placoderm-stub