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-Rhône, Hérault, 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 family, which has been only recently recognized in Late Cretaceous European deposits, will geographically and stratigraphically widen with further discoveries.
Highlights
Coelacanths, or Actinistia, are known from the Early Devonian up to the present, with only two living species, Latimeria chalumnae and L. menadoensis
In 2004, an single mawsoniid remain was found in the Late Cretaceous of Madagascar [2] and one year later, a single lower jaw bone from the terminal Cretaceous of southern France was referred to a mawsoniid coelacanth [3], extending the geographical and stratigraphical ranges of the family
Axelrodichthys is a genus previously known by two species from the early Cretaceous of Brazil, A. araripensis Maisey, 1986 and A. maiseyi Carvalho, Gallo, Santos, 2013, but some evidence indicate that this genus, as currently defined, is present in Africa [2], [4], [5], [6]
Summary
Coelacanths, or Actinistia, are known from the Early Devonian up to the present, with only two living species, Latimeria chalumnae and L. menadoensis. It is very similar to the less complete right prearticular of A. megadromos from Ventabren (Fig 6B) Both are thin bones with a subrectangular edentulous posterior lamina, which expands dorsally frontward, mirroring the general outline of the lateral angular (preserved in the holotype of A. megadromos). The teeth are very similar in size and shape to the parasphenoid teeth from Velaux (compare Fig 4 with Fig 7A), or to teeth borne by an unidentified bone from Bouc-Bel-Air (Fig 7B is a detail of the specimen illustrated in Fig 2L), i.e. they are small, hemispherical and marked by fine striations that radiate from the apex These features indicate that this piece likely belongs to a mawsoniid, likely a fragment of parasphenoid
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