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Protopteraspididae
Protopteraspididae is an extinct family of pteraspidid heterostracan agnathans. Fossils of the various genera are found in early Devonian-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 group of various transitional forms representing a gradual transition between the more advanced Pteraspoidei (comprising Pteraspididae, Gigantaspis and Protaspididae),[1] and the anchipteraspidids and the Psammosteids. GeneraProtopteraspids are found in Lower Devonian marine strata of the Western United States, Northern Canada, England, France, Belgium, Svalbard, Norway, and Podolia, Ukraine.[2] ProtopteraspisThis genus is known from several species from Lower Devonian England, France and Belgium DoryaspisThis 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 Svalbard. EscharaspisMiltaspisStegobranchiaspisUnarkaspis"Trygonaspis""Trygonaspis" is a nomen nudum 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.[citation needed] References
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