New Early Miocene hystricognath rodents (Caviomorpha) from the Madre de Dios River in the southeastern Peruvian Amazon
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2026-03-01
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South American hystricognath rodents (Caviomorpha) are a dynamic and important group of mammals with a rich fossil record that spans nearly every continental ecosystem. The oldest records come from the Palaeogene of the Peruvian Amazonia. They are well-documented in the Early Miocene assemblages from extratropical Patagonia. In this work, we describe the first Early Miocene caviomorph assemblage (AMD-45) from the tropics that is both abundant and taxonomically rich, enabling us to evaluate early biogeographic patterns and dispersal events influencing this clade. Nine taxa belonging to the four caviomorph superfamilies, as well as a caviomorph incertae sedis are recognized. These rodents have brachydont and generalized molars (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 silbamanta sp. nov. and Maquiamys precursor), and even euhypsodont teeth (Peruchinchilla prima gen. et sp. nov.). The AMD-45 fauna represents a mix of generalized and derived taxa, with chinchilloids and pan-octodontoids being the most taxonomically diverse and abundant. Comparison with other South American rodent assemblages supports the hypothesis that the equatorial tropics acted as a taxonomic incubator (long-lasting lineages) and provides evidence for in situ evolution and migration waves. The AMD-45 rodents also represent the oldest occurrence of high-crowned caviomorphs in low-latitude faunas, with the evolution of hypsodonty proposed to follow distinctive latitudinal and temporal trajectories.
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Arnal, M, RF Kay, LA Valdivia, W Salenbien, PE Morse, MR Borths, BA Williams, C Riddle, et al. (2026). New Early Miocene hystricognath rodents (Caviomorpha) from the Madre de Dios River in the southeastern Peruvian Amazon. Papers in Palaeontology, 12(2). 10.1002/spp2.70064 Retrieved from https://hdl.handle.net/10161/35503.
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Richard Frederick Kay
I have two areas of research: 1) the evolution of primates in South America; and 2) the use of primate anatomy to reconstruct the phylogenetic history and adaptations of living and extinct primates, especially monkeys and apes.
1) Evolution of primates and mammalian faunal evolution, especially in South America. For the past 30 years, I have been engaged in research in Argentina, Bolivia The Dominican Republic, Peru, and Colombia with three objectives: a) to reconstruct the evolutionary history and adaptive patterns of South America primates and other mammals; b) to establish a more precise geologic chronology for the mammalian faunas between about 36 and about 15 million years ago; and c) to use anatomy and niche structure of modern mammals as a means to reconstruct the evolution of mammalian niche structure in the Neotropics.
2) Primate Anatomy. I am working to reconstruct the phylogeny of primates based (principally) on anatomical evidence; and to infer the adaptations of extinct primates based mainly on cranial and dental evidence. Recently I published a paper tracing the evolution of the primate neocortex using brain casts of living and fossil primates. We show that vision, not frontal lobe expansion, drove the evolution of large brains in primates, including humans.
Field activities
Current fieldwork is focused on the study of terrestrial biotic change in Patagonia through the 'mid-Miocene Climate Optimum' when global climate was moderate and the subtropical zone, with primates and other typically tropical vertebrates, extended their ranges up to 55 degrees of South latitude.
In this collaborative research undertaking the geochronology of the Santa Cruz Formation at in extreme southern Argentina is being refined using radiometric dating. Stratigraphically-controlled collections have been made of vertebrates and plant macro- and microfossils. Climate change and its impact on the biota is assessed by documenting changes in mammalian community structure (richness, origination and extinction rates, and ecological morphology). This evidence is compared with continental sequences in the Northern Hemisphere and oceanic climatic records to improve our understanding of the timing and character of climatic change in continental high latitudes during this temporal interval.
A second field project is the study of the fossil vertebrates of the Amazon Basin. The hope is to recover primates from the Oligocene through Early Miocene. New material will shed light on the phylogenetic status of African Paleogene anthropoids, one of which may be the platyrrhine sister-taxon. Also, new remains of fossil primates will help to refine hypotheses about the origins of the modern families and subfamilies of platyrrhines, all of which trace back to an Early Miocene (17-21 Ma) common ancestor. Finally, new fossil primates may further constrain the time of entry of platyrrhines into South America.
Blythe A. Williams
My research has focused on the evolutionary relationships (phylogenetics) and ecological adaptations of Primates from a paleontological perspective. I’m also interested in the evolutionary history of human dance. My current teaching includes Dance Science, Ethics in Evolutionary Anthropology, and Becoming Human.
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