The Neotropics harbor the most species-rich freshwater fish fauna on the planet, but the timing of that exceptional diversification remains unclear. Did the Neotropics accumulate species steadily throughout their long history, or attain their remarkable diversity recently? Biologists have long debated the relative support for these museum and cradle hypotheses, but few phylogenies of megadiverse tropical clades have included sufficient taxa to distinguish between them. We used 1288 ultraconserved element loci spanning 293 species, 211 genera, and 21 families of characoid fishes to reconstruct a new, fossil-calibrated phylogeny and infer the most likely diversification scenario for a clade that includes a third of Neotropical fish diversity. This phylogeny implies paraphyly of the traditional delimitation of Characiformes because it resolves the largely Neotropical Characoidei as the sister lineage of Siluriformes (catfishes), rather than the African Citharinodei. Time-calibrated phylogenies indicate an ancient origin of major characoid lineages and reveal a much more recent emergence of most characoid species. Diversification rate analyses infer increased speciation and decreased extinction rates during the Oligocene at around 30 Ma during a period of mega-wetland formation in the proto-Orinoco-Amazonas. Three species-rich and ecomorphologically diverse lineages (Anostomidae, Serrasalmidae, and Characidae) that originated more than 60 Ma in the Paleocene experienced particularly notable bursts of Oligocene diversification and now account collectively for 68% of the approximately 2150 species of Characoidei. In addition to paleogeographic changes, we discuss potential accelerants of diversification in these three lineages. While the Neotropics accumulated a museum of ecomorphologically diverse characoid lineages long ago, this geologically dynamic region also cradled a much more recent birth of remarkable species-level diversity. [Biodiversity; Characiformes; macroevolution; Neotropics; phylogenomics; ultraconserved elements.]

A new species of Tetragonopterus is described from the rio Jari, a tributary to the left margin of rio Amazonas, at the border between Amapá and Pará States, northern Brazil. It is morphologically diagnosed from the other species of the genus (T. argenteus, T. chalceus, and T. rarus new combination) by the lozenge-shaped spot on the caudal peduncle vs. rounded to square spot on the other species. Partial sequences of the mitochondrial gene Cytochrome Oxidase C subunit I, from representatives of all valid species of Tetragonopterus, including this new species, were analyzed. The obtained results revealed a significant genetic distance between the new species and its congeners. A discussion on the new combination, Tetragonopterus rarus, is also provided.

The family Trichomycteridae is one of the most diverse groups of freshwater catfishes in South and Central America with eight subfamilies, 41 genera and more than 300 valid species. Its members are widely distributed throughout South America, reaching Costa Rica in Central America and are recognized by extraordinary anatomical specializations and trophic diversity. In order to assess the phylogenetic relationships of Trichomycteridae, we collected sequence data from ultraconserved elements (UCEs) of the genome from 141 specimens of Trichomycteridae and 12 outgroup species. We used a concatenated matrix to assess the phylogenetic relationships by Bayesian inference (BI) and maximum likelihood (ML) searches and a coalescent analysis of species trees. The results show a highly resolved phylogeny with broad agreement among the three distinct analyses, providing overwhelming support for the monophyletic status of subfamily Trichomycterinae includingItuglanisandScleronema. Previous relationship hypotheses among subfamilies are strongly corroborated, such as the sister relationship between Copionodontinae and Trichogeninae forming a sister clade to the remaining trichomycterids and the intrafamilial clade TSVSG (Tridentinae-Stegophilinae-Vandelliinae-Sarcoglanidinae-Glanapteryginae). Monophyly of Glanapteryginae and Sarcoglanidinae was not supported and the enigmaticPotamoglanisis placed outside Tridentinae.