MORPHOGENESIS AND EVOLUTION OF CRINOIDS AND OTHER PELMATOZOAN ECHINODERMS IN THE EARLY PALEOZOIC

Abstract

The morphogenesis and homologies of the major skeletal structures of crinoids and similar Early Paleozoic echinoderms are analyzed on the basis of comparative morphological analysis. The study of symmetry and asymmetry in the structure and morphogenesis of pelmatozoan echinoderms increases the understanding of the mechanism and sequence of the early development of different types of symmetry in evolution. It is shown that the appearance and diversification of crinoids in the Ordovician played a major role in the Ordovician evolutionary radiation of the marine biota, which resulted in the appearance of many classes of marine animals that have survived until the present day. The development of the morphological organization of higher taxa of echinoderms is discussed, and evolutionary trends, from the formation of the archetype to the development of more specialized structures, are revealed. The study is based on extensive material, particularly from the Ordovician of the Baltic region.