''Deinodus'' is a

form genus Form classification is the classification of organisms based on their morphology, which does not necessarily reflect their biological relationships. Form classification, generally restricted to palaeontology, reflects uncertainty; the goal of s ...

that includes two species: the form found in the

Onondaga Formation The Onondaga Limestone is a group of hard limestones and dolomites of Devonian age that form an important geographic feature in some areas in which it outcrops; in others, especially its Southern Ontario portion, the formation can be less promine ...

of western

New York New York most commonly refers to: * New York City, the most populous city in the United States, located in the state of New York * New York (state), a state in the northeastern United States New York may also refer to: Film and television * '' ...

, ''Deinodus bennetti'', and the form found in the Columbus and Limestone of central

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 ...

, ''Deinodus ohioensis''. Both species are limited to the

Eifelian The Eifelian is the first of two faunal stages in the Middle Devonian Epoch. It lasted from 393.3 ± 1.2 million years ago to 387.7 ± 0.8 million years ago. It was preceded by the Emsian Stage and followed by the Givetian Stage. North American s ...

age of the middle

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

Period, which occurred 398-391 million years ago (Martin, 2002). Denison (1978) postulates that the genus could be an

arthrodire Arthrodira (Greek for "jointed neck") is an Order (biology), order of extinct armored, jawed fishes of the class Placodermi that flourished in the Devonian period before their sudden extinction, surviving for about 50 million years and penetratin ...

ptyctodont The ptyctodontids ("folded-teeth") are placoderms of the order Ptyctodontida, containing the family Ptyctodontidae. With their big heads, big eyes, reduced armor and long bodies, the ptyctodontids bore a superficial resemblance to modern day ch ...

, but places it in his "

incertae sedis ' () or ''problematica'' is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty ...

" section. Individual specimens tend to resemble the ptyctodonts from the same units and ptyctodonts from

Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

, so ''Deinodus'' is most likely a ptyctodont. Specimens interpreted as lateral spines may show that ''Deinodus'' was a basal ptyctodont, not far removed from the petalichthids (Martin, 2002). ''Deinodus bennetti'' was first described in 1919 (Hussakof and Bryant). Specimens of ''Deinodus'' exhibit a variety of shapes, though most possess the characteristic large tubercles reported by Hussakof and Bryant (1918). Those specimens that do not possess tubercles resemble those that do possess tubercles. These tubercles are usually found on a margin, close to the widest point, and are different in appearance from those reported in other placoderms (Long, 1997). The variety of shapes probably represents function rather than

ontogeny Ontogeny (also ontogenesis) is the origination and development of an organism (both physical and psychological, e.g., moral development), usually from the time of fertilization of the egg to adult. The term can also be used to refer to the stu ...

. Specimens have been attributed to upper and lower dental plates, dorsal spines, trunk shield plates and lateral spines. Tubercles are found on all of these elements (Long, 1997; Martin, 2002). Most specimens that are considered dental elements are still entombed in matrix, so it is difficult to determine the feeding strategy of the fish (Martin, 2002). Since most ptyctodonts are durophagus (Maisey, 1996), meaning that they ate organisms with hard shells or exoskeletons, it seems likely that ''Deinodus'' was too. ''Deinodus ohioensis'' was a bit smaller than ''D. bennetti'' and preferred shallower water. ''D. ohioensis'' could have been a smaller species or juvenile ''D. bennetti'' using the Columbus sea as a nursery area (Martin, 2002).

References

* Denison, R. 1978. Placodermi. In: Schultze, H.P. ed. Handbook of Paleoichthyology vol. 2. Gustav Fischer Verlag, Stuttgart. 128 pages. * Hussakof, L. and W.L. Bryant. 1918. Catalog of fossil fishes in the Museum of the Buffalo Society of Natural Sciences. Bulletin of the Buffalo Society of Natural Sciences 17:18-22. * Long, J.A. 1997. Ptyctodontid fishes (Vertebrata, Placodermi) from the Late Devonian Gogo Formation, Western Australia, with a revision of the European genus Ctenurella Orvig, 1960. Geodiversitas 19(3): 515–555. * Maisey, J. G. 1996. Discovering Fossil Fishes. Henry Holt, New York. 223 pages. * Martin, R. 2002. Taxonomic Revision and Paleoecology of Middle Devonian (Eifelian) Fishes of the Onondaga, Columbus and Delaware Limestones of the Eastern United States. Dissertation, West Virginia University.

External links

Taxonomic Revision and Paleoecology of Middle Devonian (Eifelian) Fishes of the Onondaga, Columbus and Delaware Limestones of the eastern United States
(PDF file) (PhD dissertation) Placodermi enigmatic taxa Placoderms of North America Devonian placoderms Paleontology in New York (state) Paleontology in Ohio Eifelian life {{Placoderm-stub