The Coelacanth Latimeria chalumnae

Abstract

Crossopterygians are a distinctive and once widespread group of fishes, first known from rocks of Devonian age. They are characterised by the possession of two dorsal fins, the cosmoid structure of their scales and dermal bones, and well-formed fleshy lobed paired fins. The internal skeleton of the latter is much concentrated so that only a single bone (humerus, femur) articulates proximally with the girdles and distally with two bones (radius and ulna, tibia and fibula). The latter are followed by the more variable distal fin supports. The most important distinguishing feature of these fishes is the division of the neurocranium into two parts, an anterior, ethmo-sphenoid portion and a posterior, otico-occipital portion with an intracranial joint between them. The large, persistent notochord inserts upon the posteroventral margin of the ethmo-sphenoid portion of the skull (Thomson 1969; Moy-Thomas and Miles 1971; Andrews 1973).