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The material of Ichthyostega Säve-Söderbergh 1932 collected by the Danish expeditions to East Greenland (1929-1955) led by Lauge Koch is described and documented by photographs of all important specimens. The ichthyostegids are related to the osteolepiforms, and comparisons with the Devonian osteolepiform fish Eusthenopteron and post-Devonian stegocephalians are made. In some respects the ichthyostegids are fish-like, whereas in others they have reached the tetrapod level. However, they also show specializations unparalleled in later tetrapods and belong to a sidebranch of the Osteolepipoda. Several new structures, such as canals for the occipital arteries, the prominent sacculus vesicle, the parotic crest of the palatoqudrate, the attachment areas for a paired basicranial muscle, and an arcual plate dorsal to the notochord are described. Special problems, e.g., the terminology of the dermal bones of the skull roof, cranial kinetism, resegmentation, the metapterygial stem, and the origin of the tetrapod limbs, are discussed. It is concluded that the hindlimb in Ichthyostega is pentadactyl and that pentadactyly is primitive for the Osteolepipoda.
Anders Erik Vilhelm Jarvik was a Swedish paleontologist who worked extensively on the sarcopterygian fish Eusthenopteron. In a career that spanned some 60 years, Jarvik produced some of the most detailed anatomical work on this fish, making it arguably the best known fossil vertebrate.
