Heterosteus
Heterosteus (Sometimes descripted as Heterostius) is an extinct genus of heterosteid placoderm known from remains discovered in Europe and Greenland. Name. "Heterosteus" is originally described as species of "Trionyx" in 1837. 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 study uses genus name "Heterostius". 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 . 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.