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

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

Lionel Cavin et al. PLoS One. 2020.

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.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1

Fig 1. Map of Southern France showing the Campanian—Maastrichthian main outcrops with the localities that have yielded mawsoniid fossil remains.

Geological information modified from

http://infoterre.brgm.fr

. The upper-left box shows the palaeogeographical reconstruction of the area in the Late Cretaceous (modified from Fondevilla et al. 2019 [40]). Stratigraphical chart showing correlations between lithostratigraphical units and the stratigraphical positions of the localities with mawsoniids remains (data from Laurent et al. 2001 [39], Tortosa 2014 [13], Fondevilla et al. 2019 [40]).

Fig 2

Fig 2. Axelrodichthys megadromos, Bouc-Bel-Air—Sousquières.

A, basisphenoid from Bouc Bel Air (CD13-Pal.2019.6.1) in posterior (1) and left lateral (2) views; B, basisphenoid of A. megadromos from Ventabren (holotype, MDE F-61) in posterior (1) and right lateral (the photograph is inversed for easier comparison) (2) views; C and D, left supratemporals (CD13-Pal.2019.6.2 and -3) in external (1) and internal (2) views; E, right supratemporal (the photographs are inversed for easier comparison) of A. megadromos from Ventabren (holotype, MDE F-61) in external (1) and internal (2) views. This specimen was misidentified as a left postparietal in Cavin et al. (2016); F, right lachrymojugal (CD13-Pal.2019.6.4) in external (1) and internal (2) views; G, left (?) squamosal (CD13-Pal.2019.6.5) in external (1) and internal (2) views, H, left quadrate (CD13-Pal.2019.6.6) in anterior view; I, right quadrate (the photograph is inversed for easier comparison) in anterolateral view of A. megadromos from Ventabren (holotype, MDE F-61); J-K, pterygoids (CD13-Pal.2019.6.7, and -8) in medial view; L, pterygoid or prearticular or parasphenoid (CD13-Pal.2019.6.9) in occlusal view; M, fragment of opercle (CD13-Pal.2019.6.11); N, preopercle (CD13-Pal.2019.6.10) in lateral view; O, fragment of cleithrum (CD13-Pal.2019.6.12) in anterior view; P, fragment of cleithrum (CD13-Pal.2019.6.13) in lateral view. Abbreviations: ant.pr, antotic process; med.w, medial wing; ot.sc.c, otic sensory canal; pop.s.c, preopercular sensory canal; pr.con, processus connectens; sph.c, sphenoid condyle; stt.com, supratemporal commissure; v.pr.Stt, ventral or descending process of the supratemporal; Thin arrows indicate openings of the sensory canals and thick arrows indicate anterior.

Fig 3

Fig 3. Axelrodichthys megadromos, Ollières—Autoroute Nord/Sud.

A, right postparietal (MHN.AIX.PV.2019.13.1) in external (1) and internal (2) views; B, right extrascapular (MHN.AIX.PV.2019.13.2) in external (1) and internal (2) views. Abbreviations: fa.i.j, facet for the intracranial joint; v.pr.Pp, ventral or descending process of the postparietal.

Fig 4

Fig 4. Axelrodichthys megadromos, Velaux—La Bastide Neuve.

Parasphenoid (MMS/VBN.09.001 G) in ventral view. Thick arrow indicates anterior. Abbreviations: lat.gr, lateral groove; med.gr, medial groove.

Fig 5

Fig 5. Axelrodichthys megadromos, Cruzy—Massecaps (M2253).

Left dentary in lateral (A) and ventral (A’) views. Abbreviations: d.p, enlarged sensory pore; lat.sw, lateral swelling.

Fig 6

Fig 6. Axelrodichthys megadromos, Fox-Amphoux—Bastide-Neuve).

A, right prearticular (collection Méchin 745) in medial view; B, right prearticular of A. megadromos from Ventabren (holotype, MDE F-61) in medial view.

Fig 7

Fig 7. Axelrodichthys megadromos, Campagne-sur-Aude—Bellevue.

A, fragment of a tooth patch, probably from a parasphenoid (MDE C3-02-57); B, Detail of teeth from a pterygoid from Bouc-Bel-Air (CD13-Pal.2019.6.9; Fig 2L) showing similar tooth morphology.

Fig 8

Fig 8. Reconstruction of the skull of Axelrodichthys megadromos.

Dark grey bones correspond to preserved elements. For missing parts (light grey), the reconstruction is based on mirror effect of the preserved parts for paired bones and on bones preserved in A. araripensis, from the Albian Santana Formation, Brazil. Labels indicate names of bones and their corresponding locality in brackets. A, Braincase in right lateral view with the left suspensorium and lower jaw in medial view; B, skull with suspensorium, cheek and opercular elements in right lateral vie; C, skull roof in dorsal view; D, ethmosphenoid portion in ventral view. Abbreviations for bones: Ang, angular; ant.pr, antotic process; Bsph, basioccbasisphenoid; Cl, cleithrum; De, dentary; Ext.l, extrascapular lateral; Ext.m, extrascapular median; Gul, gular plate; L.e, lateral ethmoid; Lj, lachrymojugal; Na, nasal; Op, opercle; Pa.a, anterior parietal; Pa.p, posterior parietal; Par, parasphenoid; Part, prearticular; p.Co, principal coronoid; Po, postorbital; Pop, preopercle; Pp, postparietal; pr.con, processus connectens; Pro, prootic; Pt, pterygoid; Q, quadrate; So, supraorbital; Spl, splenial; Sq, suamosal; Stt, supratemporal; Te, tectal. Abbreviations for localities: BAS, Bouc-Bel-Air–Sousquières; CMA, Cruzy–Massecaps; FBN, Fox-Amphoux–Bastide-Neuve; OLA, Ollières–Autoroute North/South sites; VAR, Ventabren–Aire de repos; VBN, Velaux–La Bastide-Neuve.

Fig 9

Fig 9. Simplified time-scaled phylogeny of the Mawsoniidae with their continental distribution (silhouettes).

The trichotomy between three species of Mawsonia (M. tegamensis, M. braziliensis and M. gigas) and between two species of Axelrodichthys (A. araripensis, A. megadromos) and Lualabea are not figured.

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Grants and funding

TT received a PhD CIFRE 62/2008 grant LC received a Swiss National Science Foundation grant: ‘‘Evolutionary pace in the coelacanth clade: New evidence from the Triassic of Switzerland’’ (200021-172700) G.G and X.V received a grant from the French Ministry of Education and Communication (research grant VR1013) to the Palaios association. - G.G and X.V received a grant from the Bouches du Rhône department CD 13 proposals MAPADGAC23112010-1 and MAPADGAC16012014-1-AAPC) The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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