''Aspidichthys'' ("shield fish") is a genus of large, distinctively tuberculated arthrodire placoderm of uncertain affinities from Upper Devonian marine strata in the Eastern United States and Europe.

Anatomy

The dermal surfaces of the thick bones are decorated with an irregular arrangement of large, rounded tubercles. Some specimens may display patterns of "imperfectly concentric rows." The long median dorsal plate is subrectangular in shape, and is gently bent along the midline, which tends to have a corresponding low ridge, and a posteriorly placed carinal process on the dorsal surface. In 1938, Schmidt made a restoration of ''A. ingens'' as a large-bodied, small-headed arthrodire with tremendous orbits after the now-lost holotype of that species.

Taxonomy

The taxonomic relationships of the genus remain uncertain. Miles, 1973, suggested the genus was related to the Euleptaspidae, though, this is disproved through noting the drastically different proportions of the nuchal and median dorsal plates. Schmidt's restoration of the animal as having a large body and a small head has led some paleontologists"A relationship to Holonematidae has been suggested by several paleontologists, and is possible in spite of some important differences." to suspect a relationship with the holonematids. However, this relationship is also doubtful, as the holonematids' median dorsal plates differ from those of ''Aspidichthys'' by the former being more narrower, having a low keel, and having no carinal process.

Species

''A. clavatus'' is the type species, and is known from distinctive fragments found in the

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 th ...

-aged Huron and Olentangy Shales of

Ohio Ohio () is a state in the Midwestern region of the United States. Of the fifty U.S. states, it is the 34th-largest by area, and with a population of nearly 11.8 million, is the seventh-most populous and tenth-most densely populated. The sta ...

. It has a "gently folded" median dorsal plate, and has a low crest placed on the posterior end of the median dorsal's midline. The length of the median dorsal ranges from 39 to 44 centimeters. ''A. ingens'' is a second, tremendously large species, known from Frasnian-aged strata of

Rheinland The Rhineland (german: Rheinland; french: Rhénanie; nl, Rijnland; ksh, Rhingland; Latinised name: ''Rhenania'') is a loosely defined area of Western Germany along the Rhine, chiefly its middle section. Term Historically, the Rhinelands ...

Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...

, the Holy Cross Mountains of

Poland Poland, officially the Republic of Poland, is a country in Central Europe. It is divided into 16 administrative provinces called voivodeships, covering an area of . Poland has a population of over 38 million and is the fifth-most populous ...

, Moroccan strata, and possibly from

Iran Iran, officially the Islamic Republic of Iran, and also called Persia, is a country located in Western Asia. It is bordered by Iraq and Turkey to the west, by Azerbaijan and Armenia to the northwest, by the Caspian Sea and Turkmeni ...

. The 80 centimeter-long nuchal plate is much more steeply-folded than that of ''A. clavatus''. According to Dennison 1978, the huge size of the nuchal plate makes ''A. ingens'' "the largest arthrodire in Europe."

References

Arthrodire genera Arthrodira enigmatic taxa Frasnian life Placoderms of North America Paleontology in Ohio Placoderms of Europe Fossils of Germany Fossils of Poland Devonian animals of Africa Fossils of Morocco Fossil taxa described in 1873 {{placoderm-stub