Abstract:
Notwithstanding an increase in the number of characters used in phylogenetic computer programs, cladograms produced by these methods remain debatable. There is a need to examine the phylogenetic significance of particular characters and to distinguish the most informative of them. The role of the adaptive value of characters in the understanding of the genesis of similarity between them is emphasized. It is shown that, in the reconstruction of relationships between high-rank taxa (Gnathostomata lineage), the fundamental characters of organization, which are usually excluded from consideration in cladograms, are of prime importance. These characters are the structural features of a taxon that are observed throughout its existence (for example, the structure of the olfactory apparatus, its relationship with the hypophysis, the type of ontogeny of the Gnathostomata and Cyclostomata, etc.). Based on the fundamental characters, it is concluded that the diverging trends in vertebrate evolution that gave rise to the Recent Gnathostomata and Cyclostomata were formed at the morphoevolutionary level of the Paleozoic Agnatha. The origin of the Gnathostomata is associated with the Thelodonti, which are close to the Heterostraci; the origin of the Cyclostomata is associated with the Cephalaspidomorphi.