Aim: Paleogeographic changes have had profound effects on the evolution and diversity of the Neotropical biota. However, the influence of marine incursions on the origin, diversification, and distribution of fishes is still incompletely understood. We investigate the biogeographical and chronological patterns of diversification for the marine-derived Neotropical freshwater stingrays (subfamily Potamotrygoninae) at a continental scale.Location: Neotropics, South America.Taxa: Neotropical freshwater stingrays. Subfamily Potamotrygoninae (Myliobatiformes: Chondrichthyes). Methods:We generated a time-calibrated phylogeny for 35 of the 38 valid species of Neotropical freshwater stingrays, from most of the major river basins of South America, using four genes. We used BEAST2 to determine the chronology of population and species divergence events, and "BioGeoBEARS" to infer historical biogeographic patterns. Results:The Potamotrygoninae originated during the early/middle Miocene in the upper Amazon region. We recover clades associated with particular geographic areas and detect a recurrent pattern of upper Amazon clades sister to clades in adjacent basins. The timing of dispersals from the upper Amazon to adjacent areas corresponds with the end of the Pebas wetlands. Lower Amazon and Shield associated taxa are relatively young. Main conclusions:We propose that the origin of the Neotropical freshwater stingrays is related to marine incursions that occurred during the Oligocene/Miocene. Subsequent diversification of Potamotrygoninae occurred in the Pebas wetland system in the upper Amazon with colonization of adjacent basins. These movements were generally unidirectional, with few lineages returning to the upper Amazon, and we speculate that ecological factors drove this pattern. We observed a burst of | 1407Fontenelle et al.

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The gross brain morphology, brain proportions, and position of cranial nerves in all four genera (Potamotrygon, Plesiotrygon, Paratrygon, and Heliotrygon) and 11 of the species of the Neotropical stingray family Potamotrygonidae were studied to provide new characters that may have a bearing on internal potamotrygonid systematics. The brain was also studied in four other stingray (Myliobatiformes) genera (Hexatrygon, Taeniura, Dasyatis, and Gymnura) to provide a more inclusive phylogenetic context for the interpretation of features of the brain in potamotrygonids. Our results indicate, based on neuroanatomical characters, that the genera Paratrygon and Heliotrygon are sister groups, as are the genera Potamotrygon and Plesiotrygon, agreeing with previous morphological and molecular phylogenetic studies. Both groups of genera share distinct conditions of the olfactory tracts, telencephalon and its central nuclei, hypophysis and infundibulum, morphology and orientation of the metencephalic corpus cerebelli, orientation of the glossopharyngeal nerve, and overall encephalic proportions. The corpus cerebelli of Paratrygon and Heliotrygon is interpreted as being more similar to the general batoid condition and, given their phylogenetic position highly nested within stingrays, is considered secondarily derived, not plesiomorphically retained. Our observations of the corpus cerebelli of stingrays, including Hexatrygon, corroborate that the general stingray pattern previously advanced by Northcutt is derived among batoids. The morphology of the brain is shown to be a useful source of phylogenetically informative characters at lower hierarchical levels, such as between genera and species, and thus, has significant potential in phylogenetic studies of elasmobranchs.

Potamotrygon limai, sp. nov., is described from the Jamari River, upper Madeira River system (Amazon basin), state of Rondônia, Brazil. This new species differs from congeners by presenting unique polygonal or concentric patterns formed by small whitish spots better defined over the posterior disc and tail-base regions. Potamotrygon limai, sp. nov., can be further distinguished from congeners in the same basin by other characters in combination, such as two to three rows of midtail spines converging to a single irregular row at level of caudal sting origin, proportions of head, tail and disc, patterns of dermal denticles on rostral, cranial and tail regions, among other features discussed herein. Potamotrygon limai, sp. nov., is most similar to, and occurs sympatrically with, P. scobina, and is distinguished from it by lacking ocellated spots on disc, by its characteristic polygonal pattern on posterior disc, a comparatively much shorter and broader tail, greater intensity of denticles on disc, more midtail spine rows at tail-base, and other features including size at maturity and meristic characters. Potamotrygon limai, sp. nov., is also distinguished from other species of Potamotrygon occurring in the Amazon region, except P. scobina, by presenting three angular cartilages (vs. two or one). This new species was discovered during a detailed taxonomic and morphological revision of the closely related species P. scobina, and highlights the necessity for thorough and all-embracing taxonomic studies, particularly in groups with pronounced endemism and morphological variability.

Potamotrygon scobina Garman, 1913, described from Cametá, rio Tocantins, lower Amazon basin, is taxonomically reviewed through an extensive morphological study of internal and external features. Specimens identified as P. scobina from different locations of the Amazon basin were also studied. The identity of P. scobina, its morphology, and distribution are redefined. In addition, three new species closely related to P. scobina are described from Brazil: Potamotrygon adamastor, sp. nov., from rio Uraricoera, rio Branco system, upper Amazon basin; Potamotrygon amazona, sp. nov., from rio Juruá, upper Amazon basin; and Potamotrygon garmani, sp. nov., from the mid to upper rio Tocantins. These three new species do not occur sympatrically with P. scobina, as far as known. Together with P. scobina and P. limai Fontenelle, Silva & Carvalho, 2014, the new species have three angular cartilages of different sizes, a condition not seen in any other potamotrygonin (which have either one or two angulars). Diagnostic characters in combination are primarily morphometric proportions, especially tail length and width, dermal denticles and tail thorns (their relative size, number, morphology, and distribution), tooth size and number of rows, and color pattern. Printed copy of this book is available from US$24.6 plus postage, Click here to order.

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The subfamily Potamotrygoninae, the only extant clade of elasmobranchs exclusive to freshwater environments, encompasses four genera and 38 species distributed across almost every major South American river basin. Despite their importance in the ornamental fish trade, the taxonomy and evolutionary relationships within potamotrygonines have not yet been resolved. Here, we present a comprehensive molecular phylogeny for the Neotropical freshwater stingrays, based on extensive species and population sampling (35 species and > 350 individuals from drainages across South America). Our phylogeny corroborates the monophyly of the genera Paratrygon and Heliotrygon and the monophyly of the Potamotrygon + Plesiotrygon clade. Within the Potamotrygon + Plesiotrygon clade, we identify a core Potamotrygon clade characterized by short branches, low nodal support and incongruence with current species-level taxonomy. In the core Potamotrygon clade, specimens of widespread species, such as Potamotrygon motoro and Potamotrygon orbignyi, do not form monophyletic lineages; instead, specimens from these species are often closely related to those of other species from the same river basins. These patterns could be caused by inaccurate taxonomy, hybridization, incomplete lineage sorting and rapid diversification. We discuss the conservation of Neotropical freshwater stingrays from a phylogenetic perspective and suggest ways to prioritize potamotrygonid conservation efforts with respect to endemism and evolutionary distinctiveness.

Habitat transitions are key potential explanations for why some lineages have diversified and others have not - from Anolis lizards to Darwin's finches. The ecological ramifications of marine-to-freshwater transitions for fishes suggest evolutionary contingency: some lineages maintain their ancestral niches in novel habitats (niche conservatism), whereas others alter their ecological role. However, few studies have considered phenotypic, ecological, and lineage diversification concurrently to explore this issue. Here, we investigated the macroevolutionary history of the taxonomically and ecologically diverse Neotropical freshwater river rays (subfamily Potamotrygoninae), which invaded and diversified in the Amazon and other South American rivers during the late Oligocene to early Miocene. We generated a time-calibrated, multi-gene phylogeny for Potamotrygoninae and reconstructed evolutionary patterns of diet specialization. We measured functional morphological traits relevant for feeding and used comparative phylogenetic methods to examine how feeding morphology diversified over time. Potamotrygonine trophic and phenotypic diversity are evenly partitioned (non-overlapping) among internal clades for most of their history, until 20-16 mya, when more recent diversification suggests increasing overlap among phenotypes. Specialized piscivores (Heliotrygon and Paratrygon) evolved early in the history of freshwater stingrays, while later trophic specialization (molluscivory, insectivory, and crustacivory) evolved in the genus Potamotrygon. Potamotrygonins demonstrate ecological niche lability in diets and feeding apparatus; however, diversification has mostly been a gradual process through time. We suggest that competition is unlikely to have limited the potamotrygonine invasion and diversification in South America.