Unearthing the lineage of living fossils: the oldest mawsoniid coelacanth in Europe
The study “A mawsoniid coelacanth (Sarcopterygii: Actinistia) from the Rhaetian (Upper Triassic) of the Peygros quarry, Le Thoronet (Var, southeastern France)” by Uthumporn Deesri et al., recently published in Geological Magazine, presents and describes for the first time fossil evidence for a mawsoniid coelacanth recently unearthed from a quarry in southeastern France. Their unique discovery in the marine Upper Triassic (Rhaetian) Var Department is now considered the oldest occurrence in Europe for this family of this iconic lobe-finned fish.
The enigmatic coelacanth, known only today through the single genus Latimeria, were thought extinct until accidental ‘rediscovery’ and description of these ‘living fossils’ by Miss Marjorie Courtenay-Latimer and Professor J. L. B. Smith in 1938. Since that time, only two living species of coelacanth have been found and are only observed in the Indian Ocean and around Indonesia.
Unlike their modern counterparts, fossil coelacanths have been found prior to their ‘rediscovery’ across much wider geographic regions and even freshwater habitats. The mawsoniid family of coelacanths, to which the specimen described by Deesri et al. belongs, “were thought to be present only in freshwater environments of the Cretaceous of western Gondwana (now, Africa and South America)… but which, over the last decade now, have been discovered in both marine and freshwater environments in Europe”.
This discovery was found during a French field survey in 2015 made possible through a grant from the French Centre National de la Recherche Scientifique (CNRS) and a grant from the French Embassy of Thailand to the senior author, Uthumporn Deesri. This work was first presented in August 2016 in Kitakyushu, Japan, during a workshop on extinct and living coelacanths.
The discovery of this specimen was not only special in that it is much older than previously described for European coelacanths of this family, but “…by chance, the specimen preserved two bones that are diagnostic (angular and basisphenoid)” to the specific coelacanth family. “Most representatives of the coelacanths are morphology monotonous and difficult to identify…so these remains have comparatively high palaeobiogeographical consequence”.
Coelacanths remain one of the oldest living lineages of the class Sarcopterygii, which contains all lobe-finned fish and tetrapods (including humans!), such that study of coelacanth species, their evolution, and distribution allows critical insight into the vertebrate land transition, a key step in the evolutionary history of all land-dwelling vertebrates.
The full article “A mawsoniid coelacanth (Sarcopterygii: Actinistia) from the Rhaetian (Upper Triassic) of the Peygros quarry, Le Thoronet (Var, southeastern France)” by Uthumporn Deesri, Lionel Cavin, Romain Amiot et al., is available to download free of charge for a limited time here.