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The Cocinetas Basin is located on the eastern flank of the Guajira Peninsula, northern Colombia (southern Caribbean). During the late Oligocene through the Pliocene, much of the basin was submerged. The extensive deposits in this area suggest a transition from a shallow marine to a fluvio-deltaic system, with a rich record of invertebrate and vertebrate fauna. The elasmobranch assemblages of the early Miocene to the late Pliocene succession in the Cocinetas Basin (Jimol, Castilletes and Ware formations, as well as the Patsúa Valley) are described for the first time. The assemblages include at least 30 taxa of sharks (Squaliformes, Pristiophoriformes, Orectolobiformes, Lamniformes and Carcharhiniformes) and batoids (Rhinopristiformes and Myliobatiformes), of which 24 taxa are reported from the Colombian Neogene for the first time. Paleoecological interpretations are based on the feeding ecology and on estimates of the paleohydrology (relative salinity, temperature) using stable isotope compositions of oxygen in the bioapatite of shark teeth. The isotopic composition of the studied specimens corroborates paleoenvironmental settings for the studied units that were previously estimated based on the sedimentology and biology of the taxa. These Neogene elasmobranch assemblages from the Cocinetas Basin provide new insights into the diversity the sharks and rays inhabiting the coastal and estuarine environments of the northwestern margin of South America, both during the existence of the gateway between the Atlantic and Pacific oceans and following its closure.