CETOTHERIIDAE RECORDS FROM THE LATE MIOCENE OF PATAGONIA EXPAND THE DIVERSITY OF BALEEN WHALES FROM THE SOUTHWESTERN ATLANTIC OCEAN

The marine outcrops of the Patagonian Miocene (Argentina) encompass one of the most important assemblages of fossil mysticetes recorded worldwide, including key records of extant lineages. The Patagonian Late Miocene records comprise balaenids (right whales) or cetotheriids neobalaenines (pygmy right whales). In the last years, the increase of fieldwork efforts in Miocene outcrops of Patagonia has led to the discovery of new specimens, thus expanding our knowledge of mysticetes diversity from regional and global perspectives. In this work, we describe isolated ear bones collected from the Late Miocene Puerto Madryn Formation 12–2.7 Ma (Serravalian to Piacenzian), Península Valdés (Chubut Province), preliminarily attributed to Cetotheriidae. Although the lack of diagnostic elements precludes a more precise identification (at genus or specific level) within this family, our studies reveal a previously unknown diversity of morphotypes, indicating significant taxonomic diversity among these Patagonian mysticetes. In addition, the South Atlantic cetotheriid assemblage appears to be represented exclusively by large taxa, probably of pelagic habits, which may have facilitated their dispersal into the southern basins. Finally, these records suggest a rapid dispersion of cetotheriids from the Paratethys into the Southern Hemisphere during the Late Miocene, with the Southwest Atlantic Ocean representing their southernmost limit of distribution.