Main radiation events in P an‐ O ctodontoidea ( R odentia, C aviomorpha)

Caviomorphs ( S outh A merican hystricognaths) are recorded in the continent since the middle E ocene. The middle E ocene–early O ligocene is considered a key moment for their evolutionary history because by the early O ligocene they were differentiated into four superfamilies: O ctodontoidea, C avioidea, C hinchilloidea and E rethizontoidea. Due to their generalized dental patterns and abundance in the fossil record, O ctodontoidea are interesting for analysing the origin and early history of caviomorphs. The phylogenetic relationships of the earliest octodontoids are studied herein. Results confirmed a basal caviomorph diversification in the middle E ocene ( c . 45 Mya), with one lineage leading to P an‐ O ctodontoidea, and another leading to E rethizontoidea, C avioidea and C hinchilloidea, which is not in accordance with analyses based on molecular data. Three major radiations were identified: the first one (late E ocene?/early O ligocene?) occurred in low latitudes with the differentiation of P an‐ O ctodontoidea and the earliest crown‐ O ctodontoidea. The second radiation (late O ligocene) was a large‐scale S outh A merican event; in the southernmost part of the continent it is recognized as the first P atagonian octodontoid radiation, which provided the characteristic high morphological disparity of the superfamily. The third radiation (late M iocene) is characterized by the replacement of ‘old’ by ‘modern’ octodontoids; the nature of this third event needs to be study in a broader taxonomic context. © 2015 The Linnean Society of London