Famílias hyriidae e mycetopodidae (Mollusca:Bivalvia) da Formação Solimões (Mio-Plioceno) bacia do Solimões, AM, Brasil: taxonomia, inferências paleobiogeográficas e paleoambientais.

Abstract

The Solimões Formation, situated in western Amazonia, represents the Neogene sedimentary sequence from Solimões Basin. Its is correlated to Pebas Formation in Peru and is well known for its abundant and rich fossil content, including mollusks. Research on fossil mollusks bivalves from this unit began in the 19th century, with the Gabb (1868). These organisms have calcareous bivalve shell that allow their preservation, making them valuable tools in paleoecological, paleoenvironmental, biostratigraphy and paleogeography studies. Despite the abundance and diversity of this group in western Amazonia, in Brazil there is only few studies conducted. Therefore, the present study aimed the taxonomic identification of bivalve mollusks belonging to the families Hyriidae and Mycetopodidae and to contribute in paleoenvironmental and paleoecologic interpretations, as well as the paleobiogeographic distribution of the identified fauna. The study material comprised 200 samples collected from sedimentary banks along the Jurua and Javari rivers, near Eirunepé and Atalaia do Norte towns, Amazonas State, Brazil. The taxonomic analyses allowed the identification of three genera (Castalia, Diplodon, and Prisodon) from the family Hyriidae, and one genus (Haasica) from the family Mycetopodidae. The fossil assemblage consists exclusively of freshwater taxa, indicating lacustrine and fluvial environments during the upper Miocene in the study area. The genus Castalia exhibits a wide geographical distribution, primarily in South America, with its oldest records dating to the Cretaceous. Its absence in the Paleogene may be attributed to limited studies of this period in Brazil, which focused mainly on marine basins. Meanwhile, records of the genus Diplodon span from the Jurassic to the upper Miocene. For the first time, fossil evidence of both genus Prisodon and Haasica was identified in the Miocene.