Fish otoliths from the middle Miocene Pebas Formation of the Peruvian Amazon

Abstract

A small assemblage of 22 otoliths was identified from the historical collection of Bluntschli and Peyer gathered in 1912 on the Itaya riverbank at Iquitos, Peru (Amazonia), from the Pebas Formation. The Pebas Mega-Wetland System in western Amazonia during the Miocene represented a unique, albeit short-lived, biotope characterized by a pronounced endemic evolution with gigantism in some vertebrate groups (e.g., turtles, crocodylians). Thus far, fishes have mainly been recorded based on isolated skeletal remains and teeth. Here, we describe the first well-preserved otolith assemblage from the Pebas Formation. This otolith assemblage adds a new facet to the fauna by complementing the skeletal bony fish data, primarily with species of the Sciaenidae and, to a lesser extent, Ariidae and Cichlidae. The sciaenids and ariids indicate that migration must have occurred between the marginal marine environments to the north and the Pebas Wetland System. The otoliths also indicate the likelihood of endemic developments of adapted marine immigrants to the Pebas Wetland System, some of which have become extinct (Pogonias, Umbrina), while others now represent typical South American freshwater fish groups (Plagioscion). Six new species are described based on otoliths, one in the Cichlidae—Cichlasoma bluntschlii n. sp., one in the Ariidae—Cantarius ohei n. sp., and four in the Sciaenidae—Pebasciaena amazoniensis n. gen. et n. sp., Plagioscion peyeri n. sp., Pogonias tetragonus n. sp. and Umbrina pachaula n. sp.