Heterosteus

Heterosteus (also known as Heterostius^[1][2]) 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.^[3]

Heterosteus Temporal range: Middle Devonian: Givetian, 387.7–382.7 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Life reconstruction of Heterosteus ingens
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	†Placodermi
Order:	†Arthrodira
Suborder:	†Brachythoraci
Family:	†Heterosteidae
Genus:	†Heterosteus Asmuss, 1856
Species
Heterosteus asmussi Agassiz, 1844 (type) Heterosteus ingens Heterosteus rhenanus
Synonyms
Chelonichthys asmussi

Name

Heterosteus was originally described in 1837 as species of Trionyx, a softshelled turtle.^[4] Also in later studies it was often misidentified and given names like Ichthyosauroides, Asterolepis asmussi and Chelonichthys asmusii.^[1] 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.^[1]

Life reconstruction of Heterosteus ingens

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 6 metres (19 ft 8 in).^[5] 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.

Phylogeny

Heterosteus is the type genus for the family Heterosteidae, which belongs to the superfamily Dunkleosteoidea. It is a relative of the giant Dunkleosteus, as shown in the cladogram below:^[1]

Dunkleosteoidea	Eastmanosteus calliaspis Eastmanosteus pustulosus Kiangyousteus yohii Golshanichthys asiatica Westralichthys uwagedensis Dunkleosteus raveri Dunkleosteus terrelli Dunkleosteus amblyodoratus Heterostiidae Heterosteus ingens Yinosteus major

References

1. Zhu, You-An; Zhu, Min; Wang, Jun-Qing (1 April 2016). "Redescription of Yinostius major (Arthrodira: Heterostiidae) from the Lower Devonian of China, and the interrelationships of Brachythoraci". Zoological Journal of the Linnean Society. 176 (4): 806–834. doi:10.1111/zoj.12356. ISSN 0024-4082.
2. Schultze, Hans-Peter; Cumbaa, Stephen L. (26 April 2017). "A new Early Devonian (Emsian) arthrodire from the Northwest Territories, Canada, and its significance for paleogeographic reconstruction". Canadian Journal of Earth Sciences. 54 (5): 461–476. Bibcode:2017CaJES..54..461S. doi:10.1139/cjes-2017-0013. hdl:1807/76893.
3. Denison, Robert Howland (1978). Placodermi. München [Germany]. ISBN 978-0-89574-027-4.
4. Woodward, Arthur Smith (1891). Catalogue of the fossil fishes in the British Museum (Natural History). Vol. 2. London: Printed by order of the Trustees.
5. Denison, Robert (1978). Placodermi Volume 2 of Handbook of Paleoichthyology. Stuttgart New York: Gustav Fischer Verlag. p. 66. ISBN 978-0-89574-027-4.