| Rhamphichthyoidea is a monophyletic clade of Neotropical electric fishes (Ostariophysi, Gymnotiformes), with about 55 known species, some still awaiting formal description. These species are widespread in tropical and subtropical freshwaters of South America, with a single species reaching Costa Rica in southern Central America. Rhamphichthyoid species inhabit a variety of lowland habitats including small sandy streams, floodplain oxbow lakes, and the benthos of deep river channels. Rhamphichthyoidea displays substantial morphological disparity, ranging in maximum total body size from 62 millimeters to about 1 meter, and exhibiting diversity of distinctive snout shapes. This phenotypic diversity is reflected in a broad range of ecological interactions and foraging modes. Here I studied the diversity of Rhamphichthyoidea at three levels: alpha diversity, species interrelationships, and macroevolutionary patterns. The first chapter presents results of a species level phylogeny using a total evidence approach, including a new classification based on phylogenetically diagnosed clades. The second and third chapters review the species diversity and boundaries of the poorly studied genera Rhamphichthys (7 spp.) and Gymnorhamphichthys (5 spp.). The fourth chapter presents an analysis of diversification through time, linking habitat occupancy with morphological aspects of snout shape in the radiation of Rhamphichthyoidea. In summary, this dissertation provides information on the species diversity, morphological characteristics, biogeography of the long-snouted rhamphichthyids; the phylogenetic relationships and a newly proposed classification of Rhamphichthyoidea; and adds to the understanding of general patterns of diversification within the Neotropical ichthyofauna. |
