Chapter 5: Phylogenetic Systematics of Fishes
Dahiana Arcila and Guillermo Ortí
After establishing a rather inconspicuous presence in shallow marine habitats in the early Ordovician (~480 million years ago [mya]), fishes have radiated into almost every possible aquatic habitat, displaying a spectacular array of morphological and physiological adaptations (Nelson 2006; Wainwright and Longo 2017; Sallan et al. 2018). Currently, fishes comprise the most species-rich group of living vertebrates, with over 35,000 species. Given that what we commonly refer to as “fishes” do not form a natural taxonomic assemblage (i.e., they are not a monophyletic group), their diverse forms have been appropriately assigned to three distinct groups (Nelson 2006; Nelson et al. 2016): (1) Cyclostomata (jawless fishes) are represented by about 123 living species, including the hagfishes and lampreys; (2) Chondrichthyes (cartilaginous fishes) include over 940 species represented by chimaeras, sharks, and rays; and (3) Osteichthyes (bony fishes) comprise over 34,000 species, including the ray-finned fishes (Actinopterygii) and two lineages of lobed-finned (lungfishes and coelacanth, but excluding tetrapods; all of them placed in Sarcopterygii; Figure 5.1). Dating back to the early 1700s studies by Artedi and Linnaeus, fish diversity has been cataloged on the basis of external morphological features and internal anatomy, setting up a long-lasting tradition to study the evolution of the major lineages and identifying many of the clades still recognized today (Carroll 1988; Janvier 1996). However, recently, significant changes to the structure of the current classification of fishes have been introduced by the influx of molecular evidence (Betancur-R. et al. 2013a, 2017) as a consequence of conceptual and methodological developments that will be covered in this chapter. Figure 5.1 displays the current classification of fishes based on molecular characters. Although much of the structure of this phylogenetic classification was already supported by morphological studies, resolution of most percomorph groups now classified as series (e.g., Pelagiaria, Syngnatharia, Anabantaria, Carangaria, Ovalentaria, and Eupercaria) and their inter-relationships was possible only in the light of molecular evidence. Ultimately, a comprehensive understanding of evolution requires the integration of multiple sources of information, comprising not only phenotypic data but also genetics as well as analysis of fossils and living species. In order to achieve such integration, over the last few decades the field of fish systematics has assimilated an increasing variety of molecular, morphological, and quantitative approaches for phylogenetic reconstruction (Meyer and Zardoya 2003; Mabee et al. 2007; Hilton et al. 2015; Lee and Palci 2015).