Résumé
Although the Chinchilloidea are not a species-rich clade today, they show astonishing past diversity, including the largest rodents of all time. Our goal is to infer the evolution of the first molar dimensions and the body mass in this group and to assess whether changes in these characteristics were related to diversification rates. We assembled a matrix of 11,575 characters, including both extant and extinct species. Bayesian totalevidence dating phylogenetic analyses were performed. We measured or collected from literature the length, width, and area of ml/Ml, and we computed the body mass of extinct species using recently published equations. We applied Bayesian comparative phylogenetic methods to estimate trait evolution and diversification through time. Regarding body mass, the rate of evolution accelerates slightly from the origin of the crown group (ca. 35Ma) and increases abruptly around 19-18 Ma with the emergence of the large/giant chinchilloids, until a slowdown from 9 Ma. Large body mass would have suddenly emerged in the lineage leading to the common ancestor of (Dinomyidae, tNeoepiblemidae) between 35.6 and 33.6 Ma. This suggests an absence of medium- to large-bodied ancient taxa in the fossil record. As expected, dental dimensions exhibit a similar evolutionary trend compared to body mass. Diversification analyses show that the Chinchilloidea underwent extensive early diversification. The large variation in body mass may have facilitated the initial diversification of the crown group.