Biodiversidade de roedores Caviomorpha (Rodentia: mammalia) do Mioceno na Amazônia brasileira (rio Envira, formação Solimões, Acre): aspectos morfológicos, taxonômicos e paleobiogeográficos | Biodiversity of Caviomorpha rodents (Rodentia: mammalia) from the Miocene in the brazilian Amazon (Envira river, Solimões formation, Acre): morphological, taxonomic, and paleobiogeographical aspects | Biodiversidad de roedores Caviomorpha (Rodentia: mammalia) del Mioceno en la Amazonía brasileña (río Envira, formación Solimões, Acre): aspectos morfológicos, taxonómicos y paleobiogeográficos

Caviomorpha are South American hystricognath rodents that arrived on the continent at least 40 million years ago, through a transoceanic dispersal event from Africa, most likely by rafting across the Atlantic Ocean. They are extremely diverse in taxonomy, morphology, size, and ecological habits, as well as in their evolutionary history, rapidly dispersing and diversifying soon after their arrival in South America. Caviomorpha comprise four less inclusive clades (Cavioidea, Chinchilloidea, Erethizontoidea, and Octodontoidea) all of which are widely represented in both extant and extinct faunas. In this context, the Amazon stands out as the most biodiverse region in the world for several biological groups, a pattern also reflected in the numerous fossiliferous outcrops of the Solimões Formation, where rodents are abundantly represented. Among these, the PRE06 “Coqueiros” locality, on the banks of the Envira River (State of Acre, northern Brazil), has shown significant paleontological potential – until recently largely unexplored – particularly regarding small-sized taxa, which are often absent in traditional field collections. To recover such specimens, the screen-washing technique was extensively applied, with approximately 1000 kg of sediment processed during fieldwork conducted in 2010, 2019, 2022, and 2024. Subsequently, the most complete specimens were subjected to micro-CT scanning. This technique enabled the assessment of dental wear, particularly in isolated and incomplete teeth, contributing to inferences of ontogenetic stages and to more accurate taxonomic identification. As a result, a previously unknown assemblage of both small- and large-bodied caviomorph rodents was uncovered for this region, including representatives of all four major caviomorph clades. These findings were published in two scientific articles, and a third article has been submitted. The simultaneous presence of these four clades strongly suggests the existence of a predominantly forested paleoenvironment, with well-developed wet areas, that had persisted in this region since at least the Middle Miocene. Furthermore, this thesis highlights the relevance of computed tomography as a paleontological tool for taxonomic identification, allowing non-destructive manipulation of specimens. The results presented here reinforce the role of the Brazilian Amazon as a key region for understanding the evolution and biogeography of Neotropical mammals during the Neogene and establish the PRE06 locality as one of the most promising Miocene fossil sites in South America.

Los Caviomorpha son roedores Hystricognathi sudamericanos que llegaron a este continente hace al menos 40 millones de años, a través de un evento de dispersión transoceánica desde África, probablemente cruzando el Océano Atlántico sobre balsas naturales. Son extremadamente diversos en cuanto a taxonomía, morfología, tamaño y hábitos ecológicos, así como en su historia evolutiva, ya que, una vez establecidos en América del Sur, se dispersaron y diversificaron rápidamente. Este grupo se divide en cuatro clados menos inclusivos: Cavioidea, Chinchilloidea, Erethizontoidea y Octodontoidea, todos ellos con amplia representación en faunas actuales y fósiles. En este contexto, la Amazonía se destaca como la región con mayor diversidad biológica del mundo, lo que también se refleja en los numerosos yacimientos fosilíferos de la Formación Solimões, en los cuales los roedores están ampliamente representados. Entre estos, la localidad PRE06 “Coqueiros”, a orillas del río Envira (Estado de Acre, norte de Brasil), ha demostrado un potencial paleontológico previamente poco explorado, especialmente para taxones de pequeño tamaño, frecuentemente ausentes en colectas tradicionales. Para recuperarlos, se aplicó extensamente la técnica de tamizado (screen washing), procesando aproximadamente 1000 kg de sedimento durante expediciones realizadas en 2010, 2019, 2022 y 2024. Posteriormente, los especímenes más completos fueron sometidos a microtomografía computarizada. La aplicación de esta técnica permitió estimar el desgaste dental, especialmente en dientes aislados e incompletos, contribuyendo a la evaluación ontogenética y mejorando la precisión taxonómica. Como resultado, se descubrió una fauna de roedores caviomorfos de pequeño y gran tamaño, hasta entonces desconocida para esta región, incluyendo representantes de los cuatro grandes clados de Caviomorpha. Los hallazgos fueron publicados en dos artículos científicos y un tercer artículo fue sometido. La presencia simultánea de estos cuatro clados sugiere fuertemente la existencia de un paleoambiente predominantemente boscoso, con áreas húmedas bien desarrolladas, presente en la región al menos desde el Mioceno Medio. Además, esta tesis resalta la relevancia del uso de la tomografía computarizada como herramienta paleontológica para la identificación taxonómica, al permitir la manipulación no destructiva de los especímenes. Los resultados aquí presentados refuerzan el papel de la Amazonía brasileña como una región clave para comprender la evolución y la biogeografía de los mamíferos neotropicales durante el Neógeno, consolidando la localidad PRE06 como uno de los yacimientos fosilíferos más prometedores del Mioceno en América del Sur.

Caviomorpha are South American hystricognath rodents that arrived on the continent at least 40 million years ago, through a transoceanic dispersal event from Africa, most likely by rafting across the Atlantic Ocean. They are extremely diverse in taxonomy, morphology, size, and ecological habits, as well as in their evolutionary history, rapidly dispersing and diversifying soon after their arrival in South America. Caviomorpha comprise four less inclusive clades (Cavioidea, Chinchilloidea, Erethizontoidea, and Octodontoidea) all of which are widely represented in both extant and extinct faunas. In this context, the Amazon stands out as the most biodiverse region in the world for several biological groups, a pattern also reflected in the numerous fossiliferous outcrops of the Solimões Formation, where rodents are abundantly represented. Among these, the PRE06 “Coqueiros” locality, on the banks of the Envira River (State of Acre, northern Brazil), has shown significant paleontological potential – until recently largely unexplored – particularly regarding small-sized taxa, which are often absent in traditional field collections. To recover such specimens, the screen-washing technique was extensively applied, with approximately 1000 kg of sediment processed during fieldwork conducted in 2010, 2019, 2022, and 2024. Subsequently, the most complete specimens were subjected to micro-CT scanning. This technique enabled the assessment of dental wear, particularly in isolated and incomplete teeth, contributing to inferences of ontogenetic stages and to more accurate taxonomic identification. As a result, a previously unknown assemblage of both small- and large-bodied caviomorph rodents was uncovered for this region, including representatives of all four major caviomorph clades. These findings were published in two scientific articles, and a third article has been submitted. The simultaneous presence of these four clades strongly suggests the existence of a predominantly forested paleoenvironment, with well-developed wet areas, that had persisted in this region since at least the Middle Miocene. Furthermore, this thesis highlights the relevance of computed tomography as a paleontological tool for taxonomic identification, allowing non-destructive manipulation of specimens. The results presented here reinforce the role of the Brazilian Amazon as a key region for understanding the evolution and biogeography of Neotropical mammals during the Neogene and establish the PRE06 locality as one of the most promising Miocene fossil sites in South America.