''Ohmdenia'' is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

of prehistoric

bony fish Osteichthyes (), popularly referred to as the bony fish, is a diverse superclass of fish that have skeletons primarily composed of bone tissue. They can be contrasted with the Chondrichthyes, which have skeletons primarily composed of cartilag ...

that lived from the

Toarcian The Toarcian is, in the ICS' geologic timescale, an age and stage in the Early or Lower Jurassic. It spans the time between 182.7 Ma (million years ago) and 174.1 Ma. It follows the Pliensbachian and is followed by the Aalenian. The Toarcian ...

stage of the

Early Jurassic The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic-J ...

epoch. ''Ohmdenia'' was first described in 1953 by B. Hauff, based on a

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

found in the well-known

Posidonia Shale The Posidonia Shale (german: Posidonienschiefer, also called Schistes Bitumineux in Luxembourg) geologically known as the Sachrang Formation, is an Early Jurassic (Toarcian) geological formation of southwestern and northeast Germany, northern Swit ...

Holzmaden Holzmaden is a town in Baden-Württemberg, Germany that lies between Stuttgart and Ulm. Holzmaden is 4 km south-east from Kirchheim unter Teck and 19 km south-east of Esslingen am Neckar. The A 8 runs south from Holzmaden. The town an ...

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 ...

. For a long time this animal has been considered a close relative of ''

Birgeria ''Birgeria'' is a genus of carnivorous marine ray-finned fish from the Triassic period. ''Birgeria'' had a global distribution. Fossils were found in Madagascar, Spitsbergen, Germany, Switzerland, Italy, Slovenia, China, Russia, Canada and N ...

'', a great

predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...

typical of the

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

period with an uncertain systematic position. Further studies have shown similarities with the

Pachycormiformes Pachycormiformes is an extinct order of marine ray-finned fish known from the Early Jurassic to the end of the Cretaceous. It only includes a single family, Pachycormidae. They were characterized by having serrated pectoral fins (though more rece ...

, a group considered close to the origin of teleosts and also including giant forms and planktives (e.g. ''

Leedsichthys ''Leedsichthys'' is an extinct genus of pachycormid fish that lived in the oceans of the Middle to Late Jurassic.Liston, JJ (2004). An overview of the pachycormiform ''Leedsichthys''. In: Arratia G and Tintori A (eds) Mesozoic Fishes 3 - System ...

''). Some studies have erroneously indicated ''Ohmdenia'' as a synonym of ''Saurostomus'', other studies have instead placed ''Ohmdenia'' as an important evolutionary passage between the basal pachicormiforms and the more derived planktivore pachicormiformes.Romano, C. & Brinkmann, W. 2009 Reappraisal of the lower actinopterygian ''Birgeria stensioei'' Aldinger, 1931 (Osteichthyes; Birgeriidae) from the Middle Triassic of Monte San Giorgio (Switzerland) and Besano (Italy). Neues Jahrb. Geol. P.-A. 252, 17-31. (doi: 10.1127 / 0077-7749 / 2009 / 0252-0017)

Description

This animal is known exclusively for an incomplete fossil, but sufficient to reconstruct (at least partially) its appearance. ''Ohmdenia'' must have been a large fish, at least two and a half meters long. ''Ohmdenia'' was therefore one of the largest bony fishes of the lower Jurassic, surpassed only by giant chondrostei such as ''

Strongylosteus ''Strongylosteus'' is an extinct genus of prehistoric ray-finned fish that lived during the early Toarcian age of the Early Jurassic epoch.Hennig, E. (1925). ''Chondrosteus Hindenburgi'' Pomp.---Ein «Stör» des württembergischen Ölschiefers ...

'' and ''

Gyrosteus ''Gyrosteus'' is an extinct genus of very large ray-finned fish belonging to the family Chondrosteidae. It comprises the type species, ''Gyrosteus mirabilis'', which lived during the early Toarcian (Late Early Jurassic) in what is now northern E ...

'' . The body had to be relatively slender, with a symmetrical and slender tail. The skull was long and short, and had a jaw equipped with numerous teethsmall, rather robust, rear-facing and placed in an area that extended along the dorsal margin of the jaw. The combination of a long and slender body and a low and elongated skull is unique among the fish related to ''Ohmdenia'' (the pachicormiforms).

Paleobiology

The long mouth of ''Ohmdenia'', together with the peculiar teeth, imply a particular diet for this animal. Usually, the pachicormiforms possess thin, needle-like teeth, or large fanged fangs, or are still totally devoid of teeth. ''Ohmdenia'', on the other hand, possessed numerous small backward-facing teeth; this type of dentition is commonly associated with predators that feed on

Cephalopods A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, an ...

from the soft body. Even the jaws would seem to be less robust than those of the other pachicormiforms. The presence of two fossils of belemnites in the area of the belly of ''Ohmdenia'' corroborates the theory that this animal is seen as a predator of molluscs; cephalopods with a soft body.M. Friedmann. 2012. Parallel evolutionary trajectories underlie the origin of the giant suspension-feeding whales and bony fish. Proceedings of the Royal Society B 279: 944-951

References

Pachycormiformes Early Jurassic fish Pliensbachian life Toarcian life Jurassic fish of Europe Jurassic Germany Fossils of Germany Posidonia Shale Fossil taxa described in 1953 {{Jurassic-fish-stub

Description

Paleobiology

See also

References