Caviomorph rodents were diverse and abundant components of South American mammal communities since the late Eocene. Augmenting this diversity, we describe the octodontoids of Pampa Castillo, an early Miocene site from the Galera Formation in southern Chile (Aysén Region). Six genera and eight species of octodontoids are present, two of which are new: Dudumus berggreni sp. nov. and Caviocricetus guenekko sp. nov. The octodontoids from Pampa Castillo support assignment of this fauna to the Santacrucian SALMA, consistent with previous studies.

We conducted similarity analyses on eleven early–middle Miocene Patagonian rodent faunas using hierarchical clustering. Faunas generally fell within the three South American Land Mammal ‘Ages’ (SALMAs) to which they were traditionally assigned: Colhuehuapian, Santacrucian, and ‘post-Santacrucian’. The ‘Pinturan’ is a proposed biochronologic interval between the Colhuehuapian and Santacrucian. At the generic level, Pampa Castillo clustered with ‘Pinturan’ faunas, while at the species level it clustered with the ‘typical’ faunas on which the Santacrucian SALMA is based (from outcrops of the Santa Cruz Formation along the Atlantic coast and Río Santa Cruz). The Pampa Castillo rodent fauna resembles both ‘Pinturan’ and ‘typical’ Santacrucian faunas in rodent taxon distributions, reflecting complex temporal and paleoenvironmental influences. Geochronologic data indicate that some ‘Pinturan’ sites overlap temporally with Pampa Castillo and the upper Pinturas Formation, which both clustered with ‘typical’ Santacrucian faunas. These results indicate that the ‘Pinturan’ does not represent a distinct biochronologic interval, but that the differences between it and ‘typical’ Santacrucian faunas are attributable to geographic or paleoenvironmental differences.

Occurrences of caviomorph taxa were taken from the primary scientific literature.