Formenvielfalt und Verwandtschaftsbeziehungen der Osteolepidida (Crossopterygii, Pisces)

The Middle Devonian Osteolepidinae (Thursius estonicus) are characterized as the most primitive group within the Osteolepidida, showing similarities in some of their structures with the Holoptychiida. The diversity of the later Osteolepidida is the result of radiation in connection with parallel evolution and mosaic-evolution of features in different lineages. The structural stage ofEusthenopteron foordi (Jarvik, 1942) has not been attained by some lineages, in others, however, it has been surpassed. Several lineages reached the “protetrapod”-stage. The similarities were further increased by parallel adaptation in some lineages of the Osteolepidida and of the tetrapods. The changes of the morphology during succession in time has to be considered the most objective criterion for establishing interrelationships among groups. For this reason three main groups within the crossopterygians are maintained: Rhipidistia (Holoptychiida + Osteolepidida), Onychodontia, and Actinistia.