A brief history of Caviomorph rodents as told by the fossil record

Abstract

Caviomorph rodents have a very rich 25 fossil record that provided good26 bases for understanding the major pathways of their evolution, at least in southern South27 America. The evolution of caviomorphs in intertropical South America is less known,28 although the knowledge of the Quaternary record has been improved during the last years. In29 this paper we analyze this record and describe the most important features of their30 evolutionary history. The caviomorph ancestors probably entered South America during the31 middle Eocene by rafting from Africa, and the first steps of their evolution occurred in32 intertropical areas. The evidences strongly suggest that the initial radiation of caviomorphs33 was more complex than hitherto postulated, with the differentiation of some taxa that cannot34 be assigned to any of the major clades in which caviomorphs are classically divided (the35 superfamilies Octodontoidea, Erethizontoidea, Cavioidea, and Chinchilloidea). Caviomorphs36 arrived in Patagonia during the latest Eocene or early Oligocene, and by the late Oligocene37 they were highly diversified, with representatives of the four main lineages. A great38 morphological disparity, at least in tooth morphology was then acquired mainly by the39 development of hypsodonty in several lineages. The early evolution of each of the major40 clades was also more complex than previously proposed, especially for chinchilloids and41 octodontoids. The first stages of the evolution of cavioids are more obscure because they are42 recognized through the relatively derived Deseadan species of Cavioidea s.s. Moreover, the43 steps that led to the differentiation of Dasyproctidae, Agoutidae and some Oligocene -44 Miocene forms (e.g. Neoreomys), are not known or not well understood yet. One of the most45 outstanding features of caviomorphs, the development of large size, appears as a complex46 phenomenon. Size evolved independently in multiple lines, but in what looks to be a coeval47 coordinated phenomenon.