STUDIES ON PYCNODONT FISHES (I): EVALUATION OF THEIR PHYLOGENETIC POSITION AMONG ACTINOPTERYGIANS

One of the main pending, unsolved problems concerning the study of the pycnodont fishes is their phylogenetic relationships with other major actinopterygian groups. The Pycnodontiformes have often been proposed as the sister group of the Telostei or the Teleosteomorpha. The first extensive cladistic analysis on pycnodont relationships is hereby attempted by coding Pycnodontiformes into a previously existing data matrix with major neopterygian groups: Lepisosteiformes, Semionotiformes, Macrosemiiformes, Halecomorphi, and Teleostei. This analysis has resulted on the Pycnodontiformes having an unexpected position as the most basal Neopterygii among the groups included. Therefore, pycnodonts are not the sister-group of teleosteans, and they are not holosteans either. The phylogenetic relationships and the definition of the Holostei and the Gynglimodi are not affected by the inclusion of the Pycnodontiformes, but the basal position of the latter among Neopterygii may affect the definition of this traditional major actinopterygian group. A collateral consequence of these results is that the Halecostomi can be re-defined as the clade formed by [Holostei + Teleostei]. The phylogenetic relationships of pycnodonts should, consequently, be solved among basal neopterygian groups, mostly from the Triassic, as well as relevant non-neopterygian actinopterygians in order to confirm the neopterygian affinities of the Pycnodontiformes and to verify the definition and diagnosis of the Neopterygii and the Halecostomi