Article: Homologizations of skull roofing bones between tetrapods and osteolepiform fishes

The assumption of a constant positional relationship between dermal bones and endocranial structures, which constitutes the basis for the main arguments of proponents of three suggested solutions concerning the correct homologies of the medial exocranial bones of tetrapods and osteolepiform fishes, is discussed and criticized. It is shown that, by disregarding this assumption, these homologies are easily understood. The five medial, often paired exocranial bones present in most tetrapods, except in those where the postparietals are missing, are the same five medial bones that are present in osteolepiforms if the nasals and postrostrals in these forms are fused. The homologies of the exocranial bones in Ichthyostega, and the phylogenetic position of this form are also discussed.