CONICET | Buscador de Institutos y Recursos Humanos

The phylogenetic relationships among xenarthrans, based on anatomical features, have been a subject of significant complexity due to discrepancies in results obtained by various researchers over time. However, there was some consensus regarding possible relationships at the family level. Recently, a substantial revision of these relationships within major groups has been proposed due to contributions from molecular phylogeny studies. Notable recent changes include the gliptodonts within the armadillo group and a comprehensive reordering of the sloths (Folivora). In this study, we have analyzed the mitochondrial genomes of both fossil and extant xenarthrans in search of biases in mitochondrial genome evolution through sequence alignment and analysis of the products of the 13 protein-coding genes. We have identified a bias in mitochondrial proteins, particularly among sloths, and a convergent selection between the genera Bradypus and Choloepus. These two genera were traditionally considered phylogenetically distant, yet they share a common bias attributed to their convergence in ecological niche and arboreal lifestyle. Detecting this bias, we present a novel molecular phylogeny that reaffirms the position of armadillos without significant alterations, including gliptodonts within the Chlamyphoridae. Concerning sloths, our analysis recovers Bradypus as the sister group to all sloths, consistent with anatomical approaches. Choloepus emerges as the sister group to mylodontids, aligning with recent molecular phylogenies, while caribbean sloths are placed closer to Choloepus, consistent with morphology-based proposals. The molecular phylogeny proposed here offers a novel and more congruent outcome with anatomical studies of the group.

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