First occurrence of a mawsoniid coelacanth in the Early Jurassic of Europe

Abstract

ABSTRACT—Coelacanths form a clade of sarcopterygian fishes (lobe-finned vertebrates) that today is represented by a single genus, Latimeria. This genus belongs to a lineage of marine coelacanths, the latimeriids, whose fossils are common in the Jurassic and the Cretaceous deposits of Europe and North America. During the same periods, another lineage of fresh/brackish water coelacanths, the mawsoniids, occurred in South America, Africa, and Madagascar. Mawsoniids are supposed to have originated during the Triassic in North America and were assumed to have subsequently dispersed to South America during the Jurassic, before reaching western Africa during the Early Cretaceous. Previous hypotheses advocated that mawsoniid coelacanths reached Europe during the Late Cretaceous, suggesting the dispersal of freshwater organisms from Africa to Europe during this period. We here reevaluate this scenario based on the reexamination of the coelacanth Trachymetopon from the Early Jurassic of Germany. Although this genus is known from remarkably well-preserved material, its relationships to other Mesozoic coelacanths remained unsolved. An anatomical investigation shows that Trachymetopon shares many common features with the Late Jurassic–Late Cretaceous mawsoniids Mawsonia and Axelrodichthys from western Gondwana, such as the absence of a descending process of the supratemporal, the presence of ossified ribs, and the skull roof and cheek bones ornamented by conspicuous coarse rugosities and ridges. A phylogenetic analysis of morphological characters places Trachymetopon within Mawsoniidae. We suggest that mawsoniid coelacanths were already present in Europe from the Early Jurassic onwards, challenging previous paleobiogeographic scenarios.

SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP

ACKNOWLEDGMENTS

We thank R. Bötcher (SMNS, Stuttgart, Germany), P. Havlik (GPIT, Tübingen, Germany), M. Moser (BSPG, Munich, Germany), and Z. Johanson (NHMUK, London, U.K.), for access to the coelacanth material under their care, and for the warm welcome in their respective institutions. We thank J. Bayol (École Normale Supérieure, Paris, France) for his translation of the original paper of Hennig. D. Germain (UMR 7207 CNRS-MNHN-UPMC, Paris, France) is thanked for his useful advice while using the software TNT. We thank C. Letenneur (UMR 7207 CNRS-MNHN-UPMC, Paris, France) for her reconstruction of Trachymetopon. L. Cavin (Muséum de la Ville de Genève, Switzerland) is thanked for his constructive comments on the manuscript, and for providing his revised version of the data matrix. P. Janvier (UMR 7207 CNRS-MNHN-UPMC, Paris, France), J. G. Maisey (AMNH, New York, U.S.A.), and D. R. Schwimmer (Colombus State University, Colombus, Ohio, U.S.A.) are also thanked for their useful comments on an early version of the manuscript. We thank M. Richter (NHMUK, London, U.K), who was the editor in charge of the manuscript, as well as P. Brito (Rio de Janeiro State University, Brazil) and another anonymous reviewer for their useful comments, which greatly improved the manuscript. This work is a contribution to the ANR TERRES Programme (ANR-2010-BLAN-607-03).