[Evidence for evolutionary changes in ontogeny: paleontological, comparative-morphological, and molecular aspects].

It has been noted that the integration of modern data of paleontology, comparative morphology, developmental biology, and molecular genetics forms the basis for understanding the mechanisms of evolutionary transformations of ontogeny. Paleontological and morphological evidence of the evolutionary changes in ontogeny are considered based on the data of cell and molecular biology and developmental genetics. It is shown that reorganizations of gene regulatory cascades (primarily Hox genes) play a key role in the evolution of the axial organization of animals and modifications of the limb structure of metazoans, whereas the emergence and development of new types of structures was apparently determined by the emergence of new populations of stem cells in embryogenesis (for example, neural crest cells in the evolution of vertebrates).

[The anteroposterior axis in echinoderms and displacement of the mouth in their phylogeny and ontogeny].

The difference in the position of the anteroposterior axis in larval and adult echinoderms is related to the displacement of the mouth from the anterior end of the body to the posterior end in the phylogeny of echinoderms, which occurred in the course of the reorganization of their body plan from bilateral asymmetrical to radiosymmetrical. Traces of this phylogenetic process have been especially fully preserved in the ontogeny of crinoids. Other recent echinoderms have largely lost such traces. Dislocation of Hox-genes in sea urchins, resulting from the translocation of these genes to the 5' end of the chromosome and inversion of the anterior Hox-genes, is explained by the necessity to preserve the spatial and temporal colinearity in the course of the convergence of the starting and final stages of the mouth displacement process, similar to the elevation process in crinoids, and inclusion in the basic body plan of the structure of a rudiment now regulated directly by the anterior Hox-genes.

[From Vendian to Cambrian: the beginning of morphological disparity of modern Metazoan phyla].

Continuity of the transition from Precambrian to the Phanerozoic metazoan fauna at the phylum level is analyzed. The discrete traces of feeding on bacterial mats by Dickinsonia and similar organisms are explained by extracorporeal digestion, characteristic ofa placozoan level of organization, as in the extant Trichoplax. The absence of a morphologically developed anterior end of the body, of food-gathering appendages of any kind, and of appendages responsible for movement suggest that these animals were at this level of organization. Probably, an expanded placozoan level of organization can be assumed for most vendian animals. Against this background, new characters emerged in the Cambrian to be included in the body plan of extant animal phyla. The relationships between the morphological archetype (body plan) and morphogenetic archetype are considered. It is shown that major features of a morphogenetic archetype could be retained from the time the taxon was formed.

[The role of heterochrony in the establishment of archetype in higher Echinoderm taxa].

The analysis based on paleontological data shows that the body plans of higher echinoderm taxa were established through the combination of previously developed characters. These combinations appeared due to various heterochronies and resulted in more or less complete filling of the morphological space of logical capabilities. The maximum rank of new taxa decreased with time. New body plans of higher taxa did not replace the old plans but rather overlay them, extending the hierarchy of body plans and the respective hierarchy of taxa. The macroevolution of echinoderms and other metazoans progressed from the formation of an archetype (a general body plan) to individual details, the development of structural plans of lower levels. Heterochrony resulted in mosaic evolution and obscurity of intermediate forms.