''Trachymetopon'' is an extinct genus of prehistoric coelacanth from the

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...

of Europe. Fossils have been found in the Early Jurassic

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 ...

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 ...

the

Middle Jurassic The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from about 174.1 to 163.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relatively rare, but geological formations co ...

Marnes de Dives The Marnes de Dives is a geological formation in Normandy, France. It dates back to the upper part of the Callovian stage of the Middle Jurassic.Weishampel, David B; et al. (2004). "Dinosaur distribution (Middle Jurassic, Europe)." In: Weishampel, ...

France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...

, and probably the Late Jurassic Kimmeridge Clay of England. Only one species has been named, ''Trachymetopon liassicum'', described by Henning in 1951 from an almost complete specimen found in the Lower

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 ...

Ohmden Ohmden is a municipality in the district of Esslingen in Baden-Württemberg in Germany. Neighboring communities Neighboring municipalities are starting from North clockwise: Schlierbach, Hattenhofen, Zell unter Aichelberg , all district Göpp ...

Baden-Württemberg Baden-Württemberg (; ), commonly shortened to BW or BaWü, is a German state () in Southwest Germany, east of the Rhine, which forms the southern part of Germany's western border with France. With more than 11.07 million inhabitants across a ...

.Hennig, E. (1951). Trachymetopon liassicum, Ald., ein Reisen-Crossopterygier aus Schwäbischem Ober-Lias. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen, Stuttgart, 94, 67-79. Another specimen is known from the same site, and two older specimens come from the Sinemurian of

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 ...

. The holotype of this species is in length. A giant specimen of an undetermined species of ''Trachymetopon'' found at the Middle Jurassic (Late Callovian) Falaises des Vaches Noires of

Normandy Normandy (; french: link=no, Normandie ; nrf, Normaundie, Nouormandie ; from Old French , plural of ''Normant'', originally from the word for "northman" in several Scandinavian languages) is a geographical and cultural region in Northwestern ...

. This specimen, composed of a 53 cm long palatoquadrate, belongs to an individual in length. A basisphenoid found in a museum in Switzerland that likely originates from the same locaity probably belonged to an individual around long, making ''Trachymetopon'' the largest of all coelacanths alongside ''

Mawsonia ''Mawsonia'' may refer to: * ''Mawsonia'' (fish), an extinct genus of prehistoric coelacanth fish which lived during the Cretaceous period * ''Mawsonia'' (fungus), a genus of fungi within the family Lichinaceae {{genus disambiguation ...

''. A study published in 2015 revealed that this coelacanth belongs to the Mawsoniidae. ''Trachymetopon'' is one of the few known mawsoniids to have been exclusively marine (with an indeterminate form from 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 ...

of France), while most of the other members of the group have lived in

fresh Fresh or FRESH may refer to: People *DJ Fresh (born 1977), UK-based drum and bass artist *DJ Fresh (producer), US-based R&B producer born Marqus Brown Arts, entertainment, and media Films * ''Fresh'' (1994 film), a crime film * ''Fresh'' (200 ...

and

brackish Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuari ...

waters.

Phylogeny

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

analysis of the mawsoniids published in 2020 found a polytomy grouping together ''Trachymetopon'' and the Cretaceous genera “''

Lualabaea ''Lualabaea'' is an extinct genus of prehistoric coelacanth, belonging to the family Mawsoniidae, containing the single species ''L. lerichei.'' It has been found in Late Jurassic or Berriasian aged deposits in the Democratic Republic of the Con ...

''”, '' Axelrodichthys'', and ''

''. The genus “''Lualabaea''” could be congeneric with ''Axelrodichthys''.

References

Prehistoric lobe-finned fish genera Toarcian life Jurassic fish of Europe Jurassic Germany Fossils of Germany Posidonia Shale {{Jurassic-fish-stub Mawsoniidae

Phylogeny

See also

References