The Réalmont Basin is a small, fault-bounded sedimentary depression in the Tarn department, measuring just seven kilometres from north to south and 2.5 kilometres from east to west. Like dozens of similar basins scattered across the remnants of the Variscan orogeny, it formed within the interior zones of the ancient mountain chain that assembled during the late Palaeozoic. Sediments accumulated in alluvial fans, floodplains, and shallow lakes, preserving a snapshot of continental ecosystems at the Carboniferous-Permian transition. Until now, the only hints of fossil life from this basin were mentions of plant fragments and unidentified fish scales recorded in unpublished reports from the 1970s, which later publications repeated without further detail.

That changed when prospections in 2025 and 2026 at the Cantemerle locality, where the Cantemerle Formation outcrops along a roadside, brought to light a rich collection of vertebrate remains now housed at the Muséum d’Histoire Naturelle de Toulouse. The fossils come from finely laminated black shales interbedded with sandstones, interpreted as deposits of a lacustrine environment periodically interrupted by coarse alluvial debris flows. The articulated fish skeletons are concentrated at the base of one of these shale layers, suggesting rapid burial events that entangled whole bodies before decay could scatter the bones.

Among the most striking finds is a partially preserved fin spine belonging to a hybodontiform shark of the so-called Lissodus morphotype. The spine, measuring an estimated 35 to 45 millimetres in total length, displays smooth longitudinal costae, a strong anterior keel, and a single median row of hooked denticles along its posterior face. These features are characteristic of Palaeozoic hybodontiforms traditionally assigned to the genus Lissodus, though the authors caution that a comprehensive revision of Palaeozoic material has never been undertaken. The Réalmont spine shows a unique combination of seven proximal costae and approximately twelve denticles per centimetre, differing from all comparable Palaeozoic species, and is therefore conservatively assigned to Hybodontiformes indeterminate pending additional remains.

Equally significant is a suite of acanthodid remains, including cranial fragments, scapulocoracoids, fin spines, gill rakers, branchiostegal rays, and several partial postcranial skeletons. Acanthodians, often called spiny sharks, were toothless zooplanktivores that persisted into the early Permian in European freshwater basins. The Réalmont specimens share the combination of a bent, toothless mandibular splint, an inverted Y-shaped scapulocoracoid, smooth sabre-shaped fin spines with a longitudinal groove, and small rhombic scales that define the European Stephano-Permian acanthodids Acanthodes and Westrichus. However, the absence of complete specimens and the plesiomorphic nature of most preserved characters prevent a specific identification, and the material is assigned to Acanthodidae indeterminate.

The centrepiece of the discovery, however, is an abundance of material belonging to the ray-finned fish Progyrolepis cf. heyleri. This predatory actinopterygian, which could reach 70 to 80 centimetres in length, is represented by a fragment of maxilla bearing the diagnostic vermicularly curved ridges of the genus, isolated conical teeth with ornamented ganoine collars, five postcranial skeletons showing signs of skeletal immaturity, and hundreds of isolated scales. The scales display a distinctive ornamentation of diagonally oriented ridges that divide each scale into anteroventral and posterodorsal halves, a pattern shared with the macrodont predatory fish of the late Variscan basins. The postcranial skeletons preserve details of the anal, dorsal, and caudal fins, including basal fulcral scales and grooved lepidotrichia segments, matching the anatomy described for Progyrolepis heyleri from the Bourbon-l’Archambault and Brive basins in central France.

Perhaps the most evocative specimens are four black, shiny coprolites, fossilised faeces, recovered from the same layers. Micro X-ray fluorescence analysis conducted at the Museum für Naturkunde Berlin revealed that the coprolitic matrix is composed primarily of calcium and phosphorus, consistent with calcium phosphate minerals, in sharp contrast to the aluminium, silicon, and iron of the surrounding sediment. Embedded within the matrix of one coprolite are three quadrangular scales whose ornamentation is identical to the mid-body flank scales of Progyrolepis cf. heyleri. The absence of a spiralled structure, which would be expected from a chondrichthyan producer, combined with the crushing dentition of the Lissodus-type shark, points to Progyrolepis itself as the most plausible producer. If correct, this would suggest that the Réalmont predator was not only hunting other fish but consuming members of its own kind, an early hint of cannibalism in a Palaeozoic freshwater ecosystem.

The faunal assemblage also carries important biostratigraphic weight. Progyrolepis heyleri is known only from the early Autunian of the French Massif Central, in deposits lying just above the Autunian-Stephanian C boundary. In the Buxières Formation of the Bourbon-l’Archambault Basin, the vertebrate-bearing level has been radiochronologically dated to 298.592 plus or minus 0.075 million years ago, an early Asselian age close to the Carboniferous-Permian boundary. The presence of the same fish in the Cantemerle Formation confirms the early Autunian age previously proposed on the basis of the macroflora, anchoring the Réalmont Basin firmly in the earliest Permian.

Beyond dating, the discovery reshapes our understanding of Progyrolepis itself. A critical review of the genus’s fossil record reveals that several historical attributions are invalid. The species Progyrolepis tricessimalaris from the early Permian of Texas differs fundamentally from the genus in its cranial anatomy and must be excluded. Fragmentary remains from New Mexico and Colorado lack the diagnostic characters of Progyrolepis and should be treated as indeterminate actinopterygians. Even the long-cited occurrence of Progyrolepis speciosus in the Puertollano Basin of Spain, never described or illustrated, requires verification. When these questionable records are removed, Progyrolepis emerges as a genus restricted to the Stephanian B through early Autunian of the Bohemian Massif and the French Massif Central, with P. speciosus in Bohemia and P. heyleri in France.

This restricted but still substantial distribution challenges a broader pattern. Most families of late-Variscan actinopterygians, including the amblypterids, igornichthyids, and elonichthyids, exhibit strong species-level endemism, with individual species confined to single basins or small clusters of neighbouring basins. The pronounced endemism of these small-bodied fish has been linked to their size, which implies high rates of evolution and rapid local differentiation. Progyrolepis, by contrast, spans both the French and Bohemian massifs, suggesting that its larger body size and correspondingly lower evolutionary rate allowed it to maintain wider geographic ranges even as the landscape dynamics of the Variscan range provincialised its species into separate French and Bohemian populations.

The affinities of Progyrolepis have also been clarified. Previous classifications placed it among the Palaeoniscidae, a wastebasket group, or within the Pygopteridae and Acrolepidae, but the new material and a review of skull anatomy show that these placements are untenable. Recent cladistic analyses of late Variscan actinopterygians place Progyrolepis in a clade of macrodont taxa alongside Briveichthys chantepieorum and the Elonichthyidae, sharing characters such as a large flat maxilla, two rows of marginal teeth, numerous branchiostegal rays, and identical scale ornamentation. The authors refrain from formally assigning Progyrolepis to the Elonichthyidae, noting differences in the lacrimal bone, the absence of a presupracleithrum, and the shape of the maxilla, but the possibility of a close evolutionary link between all Variscan macrodont forms is now firmly on the table.

Finally, the palaeobiogeographic implications of the Réalmont assemblage are profound. The ichthyofauna of the Cantemerle locality is identical to that of the Buxières-les-Mines locality in the Bourbon-l’Archambault Basin, demonstrating an active aquatic connection between the northern and southern basins of the French Massif Central during the early Autunian. At a larger scale, the similarity between the Réalmont fauna and that of the Bohemian basins, where Lissodus and Progyrolepis speciosus co-occur in the Stephanian C, indicates a direct dispersal corridor between the French Massif Central and the Bohemian Massif. Because none of these basins were connected by marine routes at this time, the dispersal must have occurred through continental freshwater pathways, painting a picture of interconnected lake systems threading through the Variscan highlands that allowed large predatory fish to move across hundreds of kilometres of ancient mountain terrain.

Subject of Research: Early Permian fossil fish assemblage and coprolites from the Réalmont Basin, France, and their palaeobiogeographic and taxonomic implications

Article Title: New palaeontological remains from the early Permian Réalmont Basin (Tarn, France): implications for late-Variscan palaeobiogeography and Progyrolepis taxonomy ( Actinopterygii )

Article References: New palaeontological remains from the early Permian Réalmont Basin (Tarn, France): implications for late-Variscan palaeobiogeography and Progyrolepis taxonomy ( Actinopterygii ). (n.d.). https://doi.org/10.3897/fr.29.197176

Image Credits: AI Generated

DOI: 10.3897/fr.29.197176

Keywords: Progyrolepis, Réalmont Basin, early Permian, Variscan Belt, palaeobiogeography, actinopterygii, hybodontiform, acanthodid, coprolites, French Massif Central, Carboniferous-Permian boundary, fossil fish