Abstract
BackgroundCaviidae is a diverse group of caviomorph rodents that is broadly distributed in South America and is divided into three highly divergent extant lineages: Caviinae (cavies), Dolichotinae (maras), and Hydrochoerinae (capybaras). The fossil record of Caviidae is only abundant and diverse since the late Miocene. Caviids belongs to Cavioidea sensu stricto (Cavioidea s.s.) that also includes a diverse assemblage of extinct taxa recorded from the late Oligocene to the middle Miocene of South America (“eocardiids”).ResultsA phylogenetic analysis combining morphological and molecular data is presented here, evaluating the time of diversification of selected nodes based on the calibration of phylogenetic trees with fossil taxa and the use of relaxed molecular clocks. This analysis reveals three major phases of diversification in the evolutionary history of Cavioidea s.s. The first two phases involve two successive radiations of extinct lineages that occurred during the late Oligocene and the early Miocene. The third phase consists of the diversification of Caviidae. The initial split of caviids is dated as middle Miocene by the fossil record. This date falls within the 95% higher probability distribution estimated by the relaxed Bayesian molecular clock, although the mean age estimate ages are 3.5 to 7 Myr older. The initial split of caviids is followed by an obscure period of poor fossil record (refered here as the Mayoan gap) and then by the appearance of highly differentiated modern lineages of caviids, which evidentially occurred at the late Miocene as indicated by both the fossil record and molecular clock estimates.ConclusionsThe integrated approach used here allowed us identifying the agreements and discrepancies of the fossil record and molecular clock estimates on the timing of the major events in cavioid evolution, revealing evolutionary patterns that would not have been possible to gather using only molecular or paleontological data alone.
Highlights
Estimating the timing of evolutionary diversification events is the field of major interaction between paleontology and molecular biology
Additional support that allowed the study of relevant specimens was provided to MEP by the American Museum of Natural History (AMNH) Collection Study Grant and the Yale Peabody Museum (YPM) Ostrom Fund
If all fossils are excluded from the combined analysis, a single most parsimonious tree is found with identical topology as the one from the Bayesian analysis
Summary
Estimating the timing of evolutionary diversification events is the field of major interaction between paleontology and molecular biology. Recent attempts to reconcile the two sources of information [7,8,9,10] aimed to increase the interaction and reciprocal illumination between these two sources, rather than highlighting the conflict or disagreement between paleontological and molecular clock estimates. The integration of both sources of evidence can reveal patterns on the time and mode of the evolutionary history of a group that would not be evident using only fossils or DNA sequences. Caviids belongs to Cavioidea sensu stricto (Cavioidea s.s.) that includes a diverse assemblage of extinct taxa recorded from the late Oligocene to the middle Miocene of South America (‘‘eocardiids’’)
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