Fossilized remains of an enigmatic mawsoniid coelacanth that grew over 1 m long have been discovered by an international team of paleontologists from the United Kingdom and Uruguay.
Hypothetical life restoration of a mawsoniid coelacanth from the Kimmeridge Clay Formation. Image credit: S. Gausden.
Coelacanths are a group of large lobe-finned fishes closely related to tetrapods. They were thought to have been extinct for 66 million years, until a first living specimen was caught fortuitously in South Africa in 1938.
They first appeared in the Early Devonian epoch, diversified a little in the Devonian and Carboniferous periods, and attained a maximum of diversity in the Early Triassic.
During the Cretaceous period, coelacanths are known by two families only, the Latimeriidae, which survived to the present with the genus Latimeria, and the Mawsoniidae, which lived from the Permian to Cretaceous period.
Mawsoniid coelacanths are represented by around 10 genera known from North America, Europe, South America, Africa, Madagascar and China.
Unlike members of the Latimeriidae family, which are exclusively marine, mawsoniids were also native to freshwater and brackish environments.
Some species in Mawsonia and Trachymetopon genera are known to have exceeded 5 m in length, making them among the largest known bony fishes to have ever existed.
The newly-discovered mawsoniid coelacanth lived between 157 and 152 million years ago, during the Kimmeridgian age of the Late Jurassic epoch.
Its fossilized remains were collected from the lower part of the marine Kimmeridge Clay Formation in England.
Schematic anatomical restoration of the head of a mawsoniid coelacanth from the Kimmeridge Clay Formation in left lateral view, showing the preserved bones. Image credit: Toriño et al., doi: 10.1080/02724634.2022.2125813.
“The material is constituted by a group of bones from the head and shoulder girdle of a considerably large individual, including the left angular, left dentary, left prearticular, left palatoquadrate complex, both ceratohyals and right cleithrum,” said Dr. Pablo Toriño from the Universidad de la República de Uruguay and his colleagues from the University of Southampton and the Etches Collection Museum of Jurassic Marine Life.
“Characters such as the coarse external ornamentation of the angular, and the robustness of the quadrate and the cleithrum allow classification of the individual as a member of the Mawsoniidae, whereas the configuration of external bones of the lower jaw indicates stronger Gondwanan affinities than previously expected.”
According to the team, the new specimen belongs to the European mawsoniid genus Trachymetopon or a previously unknown genus resembling Mawsonia.
“The new individual can be referred to: (i) the genus Trachymetopon (Early-Middle Jurassic), in which case it should be assumed this genus reached the Late Jurassic, and with a morphological variability higher than previously suspected,” the authors said.
“(ii) or an unknown Mawsonia-like form was present in the Late Jurassic of Europe.”
“The last scenario puts the identification of isolated elements of European Jurassic giant mawsoniids in a new complex taxonomic and paleobiogeographic context, which will deserve further research,” they concluded.
A paper on the discovery was published in the Journal of Vertebrate Paleontology.
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Pablo Toriño et al. 2022. An enigmatic large mawsoniid coelacanth (Sarcopterygii, Actinistia) from the Upper Jurassic Kimmeridge Clay Formation of England. Journal of Vertebrate Paleontology 42 (1): e2125813; doi: 10.1080/02724634.2022.2125813
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