Diversification patterns and the origin of Cavioidea sensu stricto: fossils, ghost lineages, and molecular clock estimates

PÉREZ, M.E.; POL, D.

Las Vegas

Conferencia; 70th Meeting of the Society of Vertebrate Paleontology; 2011

Society of Vertebrate Paleontology

Cavioidea sensu stricto is broadly distributed in South America and is currently represented by cavies, maras and capybaras. These forms are divergent and include the largest body size range among rodents. Extant species are divided into three distinct lineages that define the crown group of Cavioidea s.s., which has an abundant fossil record in post-Colloncuran sediments of South America. The stem group includes an assemblage of fossil taxa re- corded from the Deseadan to the Colloncuran in the southern half of South America. The diversification patterns of Cavioidea s.s. are analyzed using calibrated phylogenies froma morphological cladistic study. Although previous studies characterized the evolution of Cavioidea s.s. along a single phyletic line, our analysis shows that the history of the group was characterized by three major radiations. The first radiation occurred during the Deseadan (late Oligocene), was previously undetected, and generated the basal cavioid Asteromys and all major lineages leading to later appearing protohypsodont species. The second radiation can be traced back to the Santacrucian (early Miocene), marking the appearance of numer- ous euhypsodont lineages. The third radiation is evidenced by the early appearance of Pro- dolichotis of Laventan age (middle Miocene) and indicates the minimum age for the origin of crown cavioids. Bayesian relaxed molecular clock estimates (using four genes of ten cavioids) provided 95% highest posterior density (HPD) for the age of this node that range between 11.6 and 24.7 Ma, with a maximum probability estimate of 17 Ma (predating the first crown fossil by 4 Ma). Such discrepancy may be caused by a violation of the molecular clock assumptions or by a faulty fossil record. The geographic distribution of Oligocene- early Miocene localities with fossil rodents is restricted to high latitudes in South America, but the first fossil crown cavioid is found in northern South America. A putative origin of this group at low latitudes, coupled with the scarcity of microvertebrate localities in the Oligocene-early Miocene in this region, may explain the discrepancy between the divergence times of crown cavioids based on the fossil record and molecular clocks.