Pan-Chinchillidae, a Once Diverse Clade

Abstract

Pan-Chinchillidae is a clade of caviomorph rodents that includes extant chinchillas (Chinchilla spp.) and mountain vizcachas (Lagidium spp.) within Chinchillinae, and the plains vizcacha (Lagostomus maximus) as the sole living member of Lagostominae. Despite its relatively low diversity in recent times, the past diversity of the group was higher (8 extinct genera and nearly 20 extinct species) and with an ancient fossil record starting in the Early Oligocene. Stem chinchillids were recorded since the Early Oligocene to the Early Miocene in Argentina, Bolivia, and Chile and were represented by the extinct genera †Eoviscaccia, †Garridomys, †Loncolicu, †Saremmys, and †Incamys. Crown Chinchillidae are recorded from the Early to Middle Miocene, including both extant subfamilies, Chinchillinae (†Miochinchilla) and Lagostominae (†Prolagostomus and †Pliolagostomus). Among extant genera, Lagostomus has been recorded since the late Middle to Late Miocene, while Lagidium has been recorded since the Pleistocene and Chinchilla since the Holocene. Five main Diversification Events (DE) can be recognized in the evolutionary history of pan-Chinchillidae. The First DE (late Eocene/Early Oligocene) gave origin to the group. The Second DE (late Early to early Late Oligocene) and Third DE (earliest Early Miocene) are related to the diversification of stem chinchillids. The Fourth DE (late Early Miocene) represents the rising of crown Chinchillidae. First to Fourth DEs match with peaks of maximum cooling, followed by progressive warming intervals. The Fifth DE (Late Miocene) is marked by the origin of the extant genus Lagostomus and was probably related to a progressive cooling and the expansion of more arid and open environments in southern South America. The appearance of euhypsodonty in crown chinchillids during the Fourth DE, contrasting with previous protohypsodont stem chinchillids, may be related to the increase of volcanic activity in nearly all the Andean chain since the Late Oligocene. The maximum estimated body mass (MEBM) for the pan-chinchillids is quite stable until the Late Miocene. The MEBM of pan-chinchillids from the Early Oligocene to the Late Miocene was between 300 and 1300 g. After the Late Miocene, the MEBM increased notably, reaching more than 5000 g in the Pliocene, 8000 g in the Late Pleistocene-Holocene, and ~9000 g with the extant plains vizcacha, Lagostomus maximus. The increase of the MEBM for the pan-Chinchillidae in the latest Late Miocene coincides with the global expansion of grasslands and the Age of the Southern Plains.