A GIANT MARINE COELACANTH FROM THE JURASSIC OF NORMANDY, FRANCE

摘要

Actinistia (coelacanths) is a clade of sarcopterygian fishes (lobe-finned vertebrates) that are first known from the Early Devonian and are now represented by a single living genus, Latimeria. Although the diversity of the group is considerably reduced today, the fossil record of coelacanths displays a remarkable diversity in terms of number of species, morphology, and ecology (Forey, 1998). Although the total length of the two Latimeria species can reach about 2 m, most of the fossil coelacanths are much smaller in size (i.e., less than 50 cm) (Forey, 1998). Nevertheless, occurrences of giant coelacanths have been reported (Wenz, 1980, 1981; Schwimmer et al., 1994; Carvalho and Maisey, 2008; Dutel et al., 2012) in the Late Jurassic-Cretaceous of North America and Gondwana. These giant coelacanths are represented by two genera, Megalocoelacanthus (Schwimmer et al., 1994; Dutel et al., 2012), which is marine and estimated to have reached 4.5 m in length, and Mawsonia, which is fresh-brackish water and estimated to range between 3.5 and 6.3 m (Wenz, 1981; Carvalho and Maisey, 2008; Medeiros et al., 2011). Interestingly, Megalocoelacanthus and Mawsonia belong to two distinct coelacanth lineages, respectively the latimeriids and the mawsoniids, showing that gigantism has evolved convergently in these Mesozoic coelacanths (Dutel et al., 2012). Moreover, very fragmentary remains also suggest the presence of large marine coelacanths in the Triassic from Spitsbergen (Stensi?, 1921), taxonomical identification of which remains uncertain (Forey, 1998). Here, we report the first occurrence of a giant marine coelacanth from the Jurassic of Europe.