Heterosteus

{{Automatic taxobox

| fossil_range = Middle Devonian: Givetian, {{Fossil range|387.7|382.7}}

| image = Heterosteus recon.png

| image_caption = Life reconstruction of Heterosteus ingens

| taxon = Heterosteus

| authority = Asmuss, 1856

| subdivision_ranks = Species

| subdivision =

Heterosteus asmussi Agassiz, 1844 (type)
Heterosteus ingens
Heterosteus rhenanus

| synonyms = *Chelonichthys asmussi

}}

Heterosteus (also known as Heterostius{{Cite journal |last1=Zhu |first1=You-An |last2=Zhu |first2=Min |last3=Wang |first3=Jun-Qing |date=1 April 2016 |title=Redescription of Yinostius major (Arthrodira: Heterostiidae) from the Lower Devonian of China, and the interrelationships of Brachythoraci |journal=Zoological Journal of the Linnean Society |volume=176 |issue=4 |pages=806–834 |doi=10.1111/zoj.12356|issn=0024-4082 |doi-access=free }}{{Cite journal |last1=Schultze |first1=Hans-Peter |last2=Cumbaa |first2=Stephen L. |date=26 April 2017 |title=A new Early Devonian (Emsian) arthrodire from the Northwest Territories, Canada, and its significance for paleogeographic reconstruction |journal=Canadian Journal of Earth Sciences |volume=54 |issue=5 |pages=461–476 |language=en |doi=10.1139/cjes-2017-0013 |bibcode=2017CaJES..54..461S |hdl=1807/76893|hdl-access=free }}) is an extinct genus of heterosteid placoderm of the Middle Devonian known from remains discovered in Europe and Greenland. According to Denison, 1978, Heterosteus might have been planktivorous, along with Homosteus, and Titanichthys.{{Cite book |last=Denison |first=Robert Howland |url=https://books.google.com/books?id=syALAQAAIAAJ&q=heterosteus |title=Placodermi |date=1978 |publisher=München [Germany] |isbn=978-0-89574-027-4 |language=en}}

Name

Heterosteus was originally described in 1837 as species of Trionyx, a softshelled turtle.{{Cite book |last1=Woodward |first1=Arthur Smith |url=https://www.biodiversitylibrary.org/item/125733 |title=Catalogue of the fossil fishes in the British Museum (Natural History) |date=1891 |publisher=Printed by order of the Trustees |volume=2 |location=London}} Also in later studies it was often misidentified and given names like Ichthyosauroides, Asterolepis asmussi and Chelonichthys asmusii. Even in recent studies, it is controversial as to whether to use genus name Heterosteus or Heterostius. According to International Code of Zoological Nomenclature, suffix ‘-ostius’ in scientific name should not be corrected as ‘-osteus’, so some studies use the genus name Heterostius.

Image:Heterosteus ingens.jpg

Description

This genus includes the largest species in the family, and are among the largest arthrodires, as well, with the type species, H. asmussi, having an estimated body length of up to {{convert|6|m|ftin}}.{{cite book|last=Denison|first=Robert|title=Placodermi Volume 2 of Handbook of Paleoichthyology|year=1978|publisher=Gustav Fischer Verlag|location=Stuttgart New York|isbn=978-0-89574-027-4|pages=66}} The genus differs from Herasmius by having the orbits on slightly longer eyestalk-like projections. The various species are found in Givetian-aged deposits in Europe and Greenland. With the except of the German H. rhenanus, all species are known from freshwater deposits: H. rhenanus is based on fragments found in a marine deposit.