The last known freshwater coelacanths: New Late Cretaceous mawsoniid remains (Osteichthyes: Actinistia) from Southern France

Abstract

Coelacanths are iconic fishes represented today by a single marine genus. The group was a little bit more diversified in the Mesozoic, with representatives in marine and continental environments in the Late Cretaceous. Here we describe isolated skull bones of the last know freshwater coelacanths found in several fossil sites from the Early Campanian to the Early Maastrichtian of Southern France (in the Departments of Aude, Bouches-du-Rhô ne, Hé rault, and Var). The sample does not allow distinguishing different species, and all material is referred to Axelrodichthys megadromos Cavin, Valentin, Garcia originally described from the locality of Ventabren in Southern France. A reconstruction of the skull is proposed. Previously unrecognized features are described, including parts of the postparietal portion of the skull, of the suspensorium and of the mandible. The new data confirm the assignation of the species to the mawsoniids, and more specifically to Axelrodichthys. A cladistic analysis scoring new character states provides a similar topology than a previous analysis, i.e. A. megadromos is placed in a polytomy with Axelrodichthys araripensis and Lualabaea lerichei, two species from the Early Cretaceous of Brazil and from the Late Jurassic of the Democratic Republic of the Congo, respectively. A. megadromos appears to have been restricted to freshwater environments, to the contrary of oldest Western Gondwanan representatives of the family that were able to live in brackish and marine waters. A. megadromos is the last representative of the mawsoniids and its occurrence in Europe is probably the result of a dispersal event from Western Gondwana that happened somewhen in the Cretaceous. Based on the available data, the mawsoniids went extinct in the mid-Maastrichthian, i.e. before the end-Cretaceous mass extinction. But it is possible that the fossil record of this

Giant Mesozoic coelacanths (Osteichthyes, Actinistia) reveal high body size disparity decoupled from taxic diversity

“…African Cretaceous mawsoniids also reached meters-long sizes 25 , 26 , but never as long as Trachymetopon or as South American mawsoniids. The sister genus of Mawsonia is Axelrodichthys , which lived for part of its time interval in sympatry with Mawsonia in Brazil 45 , and extends to the Late Cretaceous in Europe with smaller forms 46 . In Africa 'Mawsonia' lavocati has been referred to Axelrodichthys by Fragoso et al 47 , and remains of this species from the Kem Kem Group in Morocco indicate individuals up to 3.5 m long 48 .…”

“…Thus, the two genera of mawsoniid coelacanths are among the ten largest bony fish that have ever lived. Interestingly, one of these giant coelacanths, Trachymetopon , lived in sympatry in the European Callovian Sea with the largest ray-finned fish that ever lived, Leedsichthys 46 .…”

Giant Mesozoic Coelacanths (Osteichthyes, Actinistia) Reveal High Body Size Disparity Decoupled From Taxic Diversity

“…African Cretaceous mawsoniids also reached meters-long sizes 23,24 , but never as large as Trachymetopon or as South American mawsoniids. The sister genus of Mawsonia is Axelrodichthys, which lived for part of its time interval in sympatry with Mawsonia in Brazil , and extends to the Late Cretaceous in Europe with smaller forms 43 . In Africa 'Mawsonia' lavocati has been referred to Axelrodichthys by Fragoso et al 44 , and remains of this species from the Kem Kem Group in Morocco indicate individuals up to 3.5 meters long 45 .…”

The first late cretaceous mawsoniid coelacanth (Sarcopterygii: Actinistia) from North America: Evidence of a lineage of extinct ‘living fossils’

“…Alongside the latimeriid coelacanths, a second family, the mawsoniids, thrived mainly in brackish and fresh water. They occupied a large geographic area covering all of Western Gondwana (South America, Africa and Madagascar) [ 16 – 25 ], with an incursion during the Late Cretaceous into Europe [ 26 – 28 ]. The systematics of the Cretaceous mawsoniids is still uncertain, particularly at the specific level, but it is increasingly clear that two sister genera, well supported by all cladistics analyses (e.g.…”

“…The systematics of the Cretaceous mawsoniids is still uncertain, particularly at the specific level, but it is increasingly clear that two sister genera, well supported by all cladistics analyses (e.g. [ 29 , 30 ]), shared their stratigraphic range throughout the Cretaceous: Mawsonia occurred in the Late Jurassic and its range extended until the early Late Cretaceous, while Axelrodichthys is known from the late Early Cretaceous (although the ghost range of its lineage is expected to extend to the Late Jurassic if it is a sister of Mawsonia ) and became extinct in the Late Cretaceous on the basis of our current knowledge [ 28 ].…”