The early Miocene elasmobranch assemblage from Zamaca (Chilcatay Formation, Peru)

Abstract

Abstract A newly discovered elasmobranch assemblage from the fossil-bearing area of Zamaca (Chilcatay Formation, southern Peru) is described herein, providing a first comprehensive view on the early Miocene shark and ray paleocommunities of the East Pisco Basin, whose sedimentary infill represents one of the most important Cenozoic Fossil-Lagerstatten worldwide. The studied assemblage includes at least twenty-two species attributed to twelve families and five orders. Thirteen taxa are recorded for the first time from the Chilcatay Formation, and four of them are recorded for the first time from the Pacific coast of South America. The reconstructed paleoenvironmental scenario is consistent with a shallow-marine coastal area, representative of a sheltered shelfal setting, influenced by both brackish and open-ocean waters. This paleoenvironment was inhabited by a community of small mesopredator elasmobranchs that exploited the Zamaca area as a nursery ground and recruitment area. The structure of the Zamaca assemblage is mainly explained by three key-features: 1) a taxonomic composition dominated by two shark lineages, Lamniformes and Carcharhiniformes, the former being predominant; 2) the leading role played by two species, Carcharhinus brachyurus and †Cosmopolitodus hastalis, accounting for about 60% of the analyzed specimens; 3) the distinctly juvenile imprint of the entire assemblage. Striking similarities emerge between the elasmobranch assemblage from Zamaca and the late Miocene one from Cerro Colorado (Pisco Formation, East Pisco Basin), thus suggesting the persistence of a peculiar “biological enclave” driven by the concurrence of the ecological, environmental, and oceanographic factors that characterized the coast of present-day Peru during the Neogene.