Résumé
BACKGROUND: Comparative genomic data among organisms allow the
reconstruction of their phylogenies and evolutionary time scales.
Molecular timings have been recently used to suggest that environmental
global change have shaped the evolutionary history of diverse terrestrial
organisms. Living xenarthrans (armadillos, anteaters and sloths)
constitute an ideal model for studying the influence of past environmental
changes on species diversification. Indeed, extant xenarthran species are
relicts from an evolutionary radiation enhanced by their isolation in
South America during the Tertiary era, a period for which major climate
variations and tectonic events are relatively well documented. RESULTS: We
applied a Bayesian approach to three nuclear genes in order to relax the
molecular clock assumption while accounting for differences in
evolutionary dynamics among genes and incorporating paleontological
uncertainties. We obtained a molecular time scale for the evolution of
extant xenarthrans and other placental mammals. Divergence time estimates
provide substantial evidence for contemporaneous diversification events
among independent xenarthran lineages. This correlated pattern of
diversification might possibly relate to major environmental changes that
occurred in South America during the Cenozoic. CONCLUSIONS: The observed
synchronicity between planetary and biological events suggests that global
change played a crucial role in shaping the evolutionary history of extant
xenarthrans. Our findings open ways to test this hypothesis further in
other South American mammalian endemics like hystricognath rodents,
platyrrhine primates, and didelphid marsupials.