The first occurrence of a freshwater percomorph fish (Actinopterygii: Teleostei) in the Ixtapa Formation (Miocene), Chiapas, southeastern Mexico

Abstract

In this paper we describe a single and incomplete fossil fish specimen collected in the Ixtapa fossiliferous site, located at the Ixtapa municipality, near Tuxtla Gutiérrez City, Chiapas, southeastern Mexico. The Ixtapa site contains ashfall sediments deposited under fluvio-lacustrine conditions, which belong to the Upper Miocene continental sediments of the Ixtapa Formation. The fossil assemblage previously recovered in this formation includes abundant angiosperm leaves, charophytes, and aquatic gastropods, as well as terrestrial mammals including horses, rhinoceros, and proboscideans. This first fossil fish from Ixtapa is considered a member of the Subdivision Percomorphaceae because its dorsal and anal fins have unsegmented spines and its caudal fin lacks the ural centrum 2. The imperfect preservation of this specimen impedes a taxonomical determination at species level; however, this fossil reveals the occurrence of primary freshwater percomorphs in the southern end of Mexico since the Miocene-Pliocene. Hence, the present discovery constitutes an important complement to understand the freshwater fish diversity in this region through time. © 2019, Instituto de Geologã-a, Universidad Nacional Autã3noma de Mã