New Early Miocene hystricognath rodents (Caviomorpha) from the Madre de Dios River in the southeastern Peruvian Amazon

Abstract

South American hystricognath rodents (Caviomorpha) are a dynamic and important group of mammalswith a rich fossil record that spans nearly every continentalecosystem. The oldest records come from the Palaeogene ofthe Peruvian Amazonia. They are well-documented in theEarly Miocene assemblages from extratropical Patagonia. Inthis work, we describe the first Early Miocene caviomorphassemblage (AMD-45) from the tropics that is both abundant and taxonomically rich, enabling us to evaluate earlybiogeographic patterns and dispersal events influencing thisclade. Nine taxa belonging to the four caviomorph superfamilies, as well as a caviomorph incertae sedis are recognized. These rodents have brachydont and generalizedmolars (Atalayamys incertum gen. et sp. nov., Matsigenkamys ericius gen. et sp. nov., Acarechimys manumanta sp.nov.), protohypsodont and more derived molars (Ricardomys antiqua sp. nov., Manumys materdei gen. et sp. nov.,Marianamys altadens gen. et sp. nov., Luantus silbamantasp. nov. and Maquiamys precursor), and even euhypsodontteeth (Peruchinchilla prima gen. et sp. nov.). The AMD-45fauna represents a mix of generalized and derived taxa,with chinchilloids and pan-octodontoids being the mosttaxonomically diverse and abundant. Comparison withother South American rodent assemblages supports thehypothesis that the equatorial tropics acted as a taxonomicincubator (long-lasting lineages) and provides evidence forin situ evolution and migration waves. The AMD-45rodents also represent the oldest occurrence ofhigh-crowned caviomorphs in low-latitude faunas, with theevolution of hypsodonty proposed to follow distinctivelatitudinal and temporal trajectories.