Ontogenetic development of the squamation in some Palaeoniscoid fishes

Analysis of the skeleton and numerous scales of Amblypterina costata (Eichwald) and Acropholis sp. (Actnopterygii, Palaeoniscodei) from the Upper Permian of the East-European Platform permits to distinguish the stages of development of the squamation during growth. There are three main stages : juvenile, subadult and adult, each being characterized by different degrees of expression of the morphological structures, including the shape of the bony plate, the sculpture, the articulation device and the shape of the tubercles on the ganoin surface. The formation of the squamation in palaeoniscids differs from the in living teleosts by the presence of two centres of the squamation development, in the anterior part of the body and the caudal lobe, and by the longer time of development. Apart from these differences, the ontogenetic development of the squamation in these two groups proceeds in the same way.