| Summary: | International audience Among vertebrates, the sarcopterygians represent a clade characterized by a mono-basal articulation of the fins or limbs to the girdles. This group is subdivided into three extant clades: tetrapods, lungfishes and coelacanths. The latter appeared during the Early Devonian and was thought to have disappeared by the end of the Cretaceous. However, two extant coelacanth species are known so far: Latimeria chalumnae, discovered in 1938 in theMozambique Channel and L.menadoensis, discovered in 1995 of Indonesia.The coelacanth clade is well known in the fossil record with more than 40 genus with world-wide occurrences. However, the inner structure of the paired fins is poorly known with only two recored fossil species with preservation of fin endoskeletal elements (Laugia from the Triassic of Greenland, Shoshonia from the Devonian of US). Coelacanths are the nearest living marine relatives of tetrapods. Indeed, the proximal endoskeletal elements of their paired nsand of tetrapod limbs are considered as homologous.The first step of this research project aims to describe the ontogenetic development of pectoral and pelvic fins of Latimeria chalumnae. This study is based on tomographic data (CTscan, Synchrotron, MRI) of a unique ontogenetic series with five different stages. The anatomical description of the endoskeletal elements of fins during the development will be completed by dissection of paired fins of adult specimens. Preliminary results show different allometric growth ratios and ossification rates in the formation of the pectoral and pelvic fins. Comparisons between the developments of proximal endoskeletal elements of paired fins of non-tetrapod sarcopterygians and of limbs of first tetrapods will contribute to a better understanding of the evolutionary steps of the terrestrialisation in vertebrates.
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