Uncoupled diversity and disparity after faunistic turnover in caviomorph rodents


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English Understanding the relationship between species diversification and morphological variation (disparity) in evolutionary radiations is a major challenge in macroevolutionary research. While the fossil record shows that sister clades can differ markedly in species richness and morphology, the evolutionary causes underlying such differences remain unclear. Caviomorpha– a diverse clade including iconic animals such as capybaras – diversified in the Americas, and the sister clades Octodontoidea and Chinchilloidea (including spiny rats and chinchillas, respectively) provide a striking example of imbalanced evolution. These clades today vary widely in diversity with 195 extant species in the former and six extant species in the latter. However, the fossil record documents a substantially higher past diversity and disparity in Chinchilloidea, including the largest rodents ever known. Here, we combine data from extant and extinct species in these two clades to infer their evolutionary history and evaluate how evolutionary dynamics shaped their contrasting patterns of diversity and disparity. We inferred a total evidence, time-calibrated phylogeny including 149 extant and 52 extinct species, and used craniodental traits and body mass to infer morphological evolution. Our results indicate that the most recent common ancestor of Chinchilloidea and Octodontoidea lived during the late Eocene (~36.5 Ma) and that the clades diverged shortly after. The inferred ancestral body mass was small (~187 gr), but grew in range over time in Chinchilloidea, reaching its maximum body mass in the Plio-Pleistocene. Although rates of morphological evolution in Chinchilloidea were significantly higher than in Octodontoidea, these clades shared similar diversity trajectories until the beginning of the Miocene. Octodontoidea then began increasing diversity until the present, whereas Chinchilloidea diversity stagnated and dropped in the late Miocene and Pleistocene. Late Neogene and Quaternary extinctions in Chinchilloidea significantly reduced its morphological disparity, reversing a pattern of relatively higher disparity in comparison to Octodontoidea that had lasted for almost 30 million years. Our findings show a case of remarkable decoupling between species diversity and disparity, highlighting complex relationships between ecomorphological differentiation, species richness, and how they were affected by extinction events.
Faculté des sciences et de médecine
Département de Biologie
  • English
Biological sciences
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