The South American fossil record and the origin of caviomorph rodents

VUCETICH, M.G., D. VERZI, M.E. PÉREZ AND E.C. VIEYTES.

Zonguldak, Türkiye

Conferencia; 12th Rodens et Saptium, The International Conference on Rodent Biology.; 2010

Caviomorph rodents are immigrants in South America, but the moment and route of immigration are still under debate. Three different faunas contend for the position of oldest in the continent. The Tinguiririca fauna (central Chile) is not younger than 31.5 Ma and has yielded only two rodent fossils representing two different taxa. The Santa Rosa fauna (central-eastern Peru) is very rich, but its age is uncertain (late Eocene-late Oligocene?). The La Cantera fauna (south of Colhué Huapi Lake, about 45º45’ South, Argentina) has yielded six rodent species, and is about 31.1-29.5 Ma old. Rodents from La Cantera are mostly known from isolated brachyodont cheek-teeth, and from incisors with multiserial enamel, a hystricognath character. Although fragmentary, this fauna is highly informative in biochronological and biogeographical terms. The absence of rodents in La Cancha (between 33.3 and 33.7 Ma in age), a very fossiliferous level bearing numerous micromammal fossils that lies below La Cantera, suggests that the rodents arrived to the latitude of Colhué Huapi Lake during the early Oligocene, and that their arrival to the continent probably occurred not long before than this time. The geographic and temporal distribution of the oldest caviomorphs suggests a north–south initial dispersion route within South America. This route agrees with the hypothesis of an African origin via transatlantic crossing, since no hystricognaths have been found in North America.