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The neotropical freshwater family Potamotrygonidae appears to be the only stingray group that has radiated in a non-marine environment. To assess the affinities of potamotrygonids to other rays, a phylogenetic analysis was undertaken using 39 morphological characters from 18 stingray groups. The single tree produced (CI = 0·80, RI = 0·88) suggests that neotropical freshwater rays are a monophyletic group, and that within Potamotrygonidae, Paratrygon is basal to a clade composed of Plesiotrygon and Potamotrygon . The sister group to potamotrygonids was determined to be amphi-American Himantura — these taxa share synapomorphies of the ventral mandibular musculature and the hyomandibular/mandibular articulation. The topology suggests that potamotrygonids are derived from a freshwater-invading ancestor that was distributed along the northern coast of South America (Pacific and Caribbean) prior to the emergence of the isthmus of Panama. This hypothesis conflicts with parasite-based biogeographic scenarios of a strictly Pacific origin for potamotrygonids. General systematic results concerning urolophids, dasyatids, and pelagic myliobatoid stingrays are also discussed. Keywords South America Amazon fishes paleogeography parasites marine Himantura Dasyatidae Urolophidae

zoological journal of the linnean society

Systematics of myliobatoid elasmobranchs: with emphasis on the phylogeny and historical biogeography of neotropical freshwater stingrays (Potamotrygonidae: Rajiformes)