Monophyly and relationships of the Osmerae (Actinopterygii: Teleostei): Paedomorphosis as evidence for history.

Abstract

The phylogenetic relationships of the Osmerae (Pisces:Teleostei), consisting of the Osmeroidei and Argentinoidei, are examined in the context of character congruence. The Osmeroidei is monophyletic, and the historical division of osmeroids into Northern and Southern Hemisphere groups is corroborated. Two problematic taxa, the neotenic Salangidae and the monotypic Lepidogalaxias salamandroides, are hypothesized to be members of the Southern Hemisphere clade, in which reductive evolution has been common. The Northern Hemisphere clade includes the Osmeridae and the Japanese Plecoglossus altivelis. The Argentinoidei is monophyletic, and is composed of two clades, Argentinoidea and Alepocephaloidea. Evidence for monophyly of the Argentinoidei is largely drawn from anatomy of the branchial basket, and other corroborating evidence is presented. The Argentinoidea is monophyletic, and contains two clades: one including the argentinids and microstomatids; the other contains bathylagids and opisthoproctids. The Alepocephaloidea is also monophyletic, and is restricted here to a single clade, Alepocephalidae. Previous phylogenetic hypotheses have placed either the Salmonidae or the highly derived galaxioid Lepidogalaxias as the sister taxon of the Neoteleostei. It is hypothesized here that the Osmerae is the sister taxon to the Neoteleostei on the basis of two synapomorphies: presence of a postmaxillary process of the premaxilla, and loss of laminar bone on the anterior margin of the hyomandibula. The Salmonidae is the sister-group to neoteleosts plus the Osmerae; the Ostariophysi the sister group to salmonids, osmerans and neoteleosts; and the Esocae are hypothesized to be the sister-group to all other euteleosts. Evidence for relationships within euteleosts, and especially within the Osmerae, is provided by both paedomorphic (reductive) and non-reductive evidence. The conditions under which the pattern of paedomorphosis will be phylogenetically informative are explored. In this study, both types of character show about the same level of homoplasy, and are considered to be equivalent sources of evidence in phylogenetic analysis.