Protopteraspididae is an extinct

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 ...

of pteraspidid heterostracan

agnatha Agnatha (; ) or jawless fish is a paraphyletic infraphylum of animals in the subphylum Vertebrata of the phylum Chordata, characterized by the lack of jaws. The group consists of both extant taxon, living (Cyclostomi, cyclostomes such as hagfish ...

ns. Fossils of the various genera are found in early

Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...

-aged marine strata. Protopteraspidids were once thought to represent a taxon of basal pteraspidids (hence "proto") but recent evaluations demonstrate that Protopteraspididae is a

paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

group of various transitional forms representing a gradual transition between the more advanced Pteraspoidei (comprising Pteraspididae, '' Gigantaspis'' and

Protaspididae Protaspididae is an extinct family of pteraspidid heterostracan agnathans. Fossils of the various genera are found in early Devonian-aged marine strata. Protaspidids were once thought to represent a transitional form between the Pteraspididae ...

),Pernegre, Vincent N., and David K. Elliott. "Phylogeny of the Pteraspidiformes (Heterostraci), Silurian–Devonian jawless vertebrates." Zoologica Scripta 37.4 (2008): 391-403. and the anchipteraspidids and the Psammosteids.

Genera

Protopteraspids are found in Lower Devonian marine strata of the Western

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

, Northern

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, and

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.Blieck, Alain. "Les hétérostracés Ptéraspidiformes, agnathes du Silurien-Dévonien du continent Nord-Atlantique et des blocs avoisinants: Révision systématique, phylogénie, biostratigraphie, biogéographie." (1984).

''Protopteraspis''

This genus is known from several species from Lower Devonian

and

''Doryaspis''

This is a genus of aberrant pteraspidids with lower lips elongated into long, dagger-like organs of unknown function. The various species are primarily restricted to the Lower Devonian strata of

''Escharaspis''

''Miltaspis''

''Stegobranchiaspis''

''Unarkaspis''

"Trygonaspis"

"Trygonaspis" is a ''

nomen nudum In Taxonomy (biology), taxonomy, a ''nomen nudum'' ('naked name'; plural ''nomina nuda'') is a designation which looks exactly like a scientific name of an organism, and may have originally been intended to be one, but it has not been published ...

'' given to a well-preserved complete armor that strongly resembles ''Protopteraspis'' in form, but with a long, recurved dorsal spine, and orbital plates that have bookshelf-like extensions. The only known specimen was found in Northern Canada.

References

Palaeos Vertebrates entry on order Pteraspidiformes
Pteraspidiformes Devonian jawless fish Early Devonian fish Prehistoric jawless fish families Early Devonian first appearances Early Devonian extinctions {{Devonian-jawless-fish-stub