Currently, there is no standardized nomenclatural scheme for identifying and naming the bones of the snout in lower actinopterygians and specifically those fishes referred to as palaeoniscoids. A literature review reveals that the same bone names are used by different researchers to identify very different bones. This lack of homogeneity is problematic because it makes comparisons among taxa difficult, impairs our understanding of the morphological diversity of lower actinopterygians, and presents potential pitfalls when building character matrices for phylogenetic analyses. Because of the problems the absence of a standardized nomenclature scheme presents, a new set of rules for the identification of the bones of the snout of lower actinopterygians is proposed. These definitions are based on characters that are commonly preserved such as the presence of sensory canals, location of bones in relation to other bones, and whether or not the bones contribute to forming nasal openings. When numerous characters are present in a single bone, this bone is considered to be a complex bone, and the name reflects this. The new definitions are based on Remane’s criteria of similarity in position and detail and are an attempt at identifying homologous structures. The snout bones of various Devonian and Carboniferous palaeoniscoids are re-identified using this new nomenclature scheme. After that, patterns regarding the makeup of the snout in Devonian and Carboniferous palaeoniscoids emerged. The snouts of Carboniferous palaeoniscoids show much more morphological diversity than those of the Devonian forms. The phylogenetic signal of these new characters was tested with their inclusion in a phylogenetic matrix constructed to investigate the relationships of lower actinopterygians. The phylogenetic tree that resulted from analysis of this matrix has clades supported by some of the new snout characters. These results suggest that in-depth investigations into such characters are necessary to form a stronger understanding of the morphological diversity of lower actinopterygians and have implications for phylogenetic studies.
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Vol. 103 • No. 4