Phylogenetic relationships of Gasterosteiformes (Teleostei, Percomorpha)

The phylogenetic relationships of Gasterosteiformes were studied in an osteological examination of representatives of 48 genera in 41 families of eurypterygian fishes to hypothesize their systematic relationships within Acanthopterygii. The outgroup comparison method was used for polarizing characters and cladistic methods employing MacClade 3.08 and PAUP 4.0 computer programs were used for reconstructing systematic relationships of Gasterosteiformes. Monophyly of Acanthomorpha, Acanthopterygii, Percomorpha, and Smegmamorpha is supported. Mugiliformes and Atherinomorpha are shown to be each other closest relatives and together form a monophyletic group. This study shows that Synbranchiformes is the sister group of Gasterosteiformes and that Elassomatiformes (Elassomatidae) is the sister group of Synbranchiformes and Gasterosteiformes. To reflect the new phylogeny in a classification of Percomorpha, it is suggested that the series Percomorpha be divided into two subseries: Smegmamorphei and Percomorphei. Smegmamorphei consist of two infraseries: Mugilomorphea (Mugiliformes, Atheriniformes, Beloniformes, and Cyprinodontiformes) and Elassomamorphea (Elassomatiformes, Synbranchiformes, and Gasterosteiformes). Percomorphei consist of four orders: Perciformes, Scorpaeniformes, Pleuronectiformes, and Tetraodontiformes. Although no unique synapomorphy was found to unite all Gasterosteiformes, support was provided that Gasterosteiformes (including Hypoptychidae and Indostomidae) is a monophyletic group. Based on the phylogenetic analysis and synapomorphies provided for the subgroups, three suborders in Gasterosteiformes are recognized: Hypoptychoidei, Gasterosteoidei, and Syngnathoidei. Dactylopteridae is shown to be a member of Scorpaeniformes and, within the taxa examined, the sister-group of Agonidae. Although monophyly of Scorpaeniformes is supported, it is nested within Perciformes and branch support indices do not strongly support its monophyly.