Origin and Phylogenetic Interrelationships of Teleosts

The origin and the phylogenetic interrelationships of teleosts have been controversial subjects of interest ever since Greenwood et al. (1966) presented a revision of teleost phylogeny and Patterson (1973, 1977) proposed a relationship between teleosts and Amia (or Halecomorpha) and named the group Halecostomi. Many differing views exist on the fundamental problem of teleost origins and phylogeny (e. g., Olsen 1984, Nursall 1996, Gardiner et al. 1996, Arratia 1999, Inoue et al. 2003, and many others). Different taxa (Amia, Lepisosteus, Amia + Lepisosteus, ┼Pycnodontiformes, ┼Dapedium, ┼Pachycormiformes, and others) have been proposed as the sister group of teleosts. Tremendous advances have occurred in our knowledge of Halecostomi and in their major component the teleosts over the past 40 years, with many new key fossils having been studied (and many extant basal teleost clades having been traced back to the Jurassic in detailed studies by Arratia 1987, 1996, 2000). In addition to new fossils, a large number of new morphological characters have been incorporated in recent phylogenetic analyses, adding to our arsenal of approaches. However, as noted by Nelson (2006), there are still many areas of disagreement in teleost phylogeny. In recent years, molecular characters are increasingly used for assessment of actinopterygian phylogeny, sometimes conflicting with morphological data. While potentially very numerous and powerful indicators of relationships, their greatest limitation is that only a few taxa (Acipenseriformes, Amia, Lepisosteidae - all three having been proposed as the sister group of teleosts in molecular studies) can be used in the molecular search for the closest relative of the teleosts. Recently, the validity of the Halecostomi, the Halecomorphi (Amia) + teleosts, has been questioned by morphological (Grande 2005, Hurley et al. 2007) and molecular (Kikugawa et al. 2004) investigations, and the old group Holostei, comprising the Halecomorpha and the Ginglymodi (e. g., Lepisosteus), is now thought by some investigators to be monophyletic after all. Closely interwoven with the search for the sister group of teleosts is the question of interrelationships of basal teleosts. Both morphological studies (including new fossil taxa) and molecular studies have examined this question. Studies of Patterson (1977) and Patterson & Rosen (1977) placed the Osteoglossomorpha at the base of extant teleosts, a position given to Elopomorpha by Arratia (1991, 1996, 1999). Molecular analyses tend to agree with Patterson's 1977 view (e. g., Inoue et al. 2003) or else they place both taxa as the sister group to all other teleosts (Lê et al. 1993) or in an unresolved relationship. Differing views exist also on the boundaries of the teleosts (explored, e. g., by Patterson & Rosen 1977, de Pinna 1996, and Arratia 2001). The names Teleocephala (of de Pinna 1996 for the crown group of all extant teleosts) and Teleosteomorpha (of Arratia 2001 for Teleostei s. str. and their closest relatives) have been proposed to variously recognize stem-based fossils of the Teleostei. These taxonomic names reflect the translation into classification of trees resulting from different levels of phylogenetic analyses. Higher up the tree in the crown-group teleosts, Clupeomorpha and Ostariophysi have been considered by many to comprise a monophyletic group after Lê et al. (1993) and, especially, Lecointre & Nelson (1996). The resulting taxon was termed the Ostarioclupeomorpha by Arratia (1996) and the Otocephala by Johnson & Patterson (1996). This suggested relationship has not been accepted by all ichthyologists, but further testing of this hypothesis will come with new morphological and molecular data. As well as there being some uncertainty here, many other questions remain on relationships of higher teleosts, including percomorphs, providing fertile ground for investigation by ichthyologists in the future. These questions were and are at the center of the research of Gloria Arratia. To recognize her contributions to the origin and phylogeny of teleosts, the American Society of Ichthyologists and Herpetologists (ASIH) sponsored the symposium "Origin and phylogenetic interrelationships of teleosts" organized by the three editors of this volume and held at the Society's annual meeting in St. Louis on 14 July 2007. At the same meeting, Gloria Arratia was honored with the Robert H. Gibbs, Jr. Memorial Award, 2007, for her contributions to systematic ichthyology. The present state of phylogenetic knowledge of the origin of teleosts and the interrelationships of teleost groups, key issues in fish systematics, based on both morphological (of extant and fossil taxa) and molecular data were presented. Progress employing the characters and taxa and in establishing databases (morphological and molecular) were also presented and evaluated from different perspectives by many contributors in the symposium. Most of the talks given at that meeting form the basis of the papers collected in this volume, together with three additional contributions. The editors and authors are pleased to dedicate this volume to Gloria Arratia in honor of her contributions and in the hope that its contents will assist and stimulate future research on the subjects that interest her most.