Increasing until extinction: understanding Macraucheniidae body-mass evolutionary history

Body-mass evolution in extinct mammals is an important factor in understanding their diversification and niche occupation dynamics over geological time. To know how Macraucheniidae, South American native ungulates, diversified over 30 Myr, we estimated body mass for 15 genera within this family and investigated which evolutionary process best explains body-mass evolution in this lineage. For this purpose, we applied a set of body-mass estimation equations and conducted comparative phylogenetic analyses to assess the presence of phylogenetic signals and identify the best-fitting model of trait evolution. Our results show that all Macraucheniidae genera can be classified as megafauna (i.e., mammals weighing more than 44 kg). The evolutionary model that best explains body-mass diversification in this family is a directional, gradual increase over time. The subfamilies Cramaucheniinae and Macraucheniinae did not differ significantly in body-mass evolutionary rates; however, the negative relationship between body mass and temperature, together with the most parsimonious evolutionary scenario, supports temperature as the primary ecological driver of body-mass evolution in macraucheniids.