Mitogenomic relationships of placental mammals and molecular estimates of their divergences.

Molecular analyses of the relationships of placental mammals have shown a progressive congruence between mitogenomic and nuclear phylogenies. Some inconsistencies have nevertheless persisted, notably with respect to basal divergences. The current study has aimed to extend the representation of groups, whose position in the placental tree has been difficult to establish in mitogenomic studies. Both ML (maximum likelihood) and Bayesian analyses identified four basal monophyletic groups, Afroplacentalia (=Afrotheria: Hyracoidea, Proboscidea, Sirenia, Tenrecidea, Tubulidentata, Macroscelidea, Chrysochloridea), Xenarthra, Archontoglires (Primates, Dermoptera, Scandentia, Lagomorpha, Rodentia) and Laurasiaplacentalia (Lipotyphla, Chiroptera, Pholidota, Carnivora, Perissodactyla, Artiodactyla, Cetacea). All analyses joined Archontoglires and Laurasiaplacentalia on a common branch (Boreoplacentalia), but the relationship between Afroplacentalia, Xenarthra and Boreoplacentalia was not conclusively resolved. The phylogenomic hypothesis with a sister group relationship between Notoplacentalia (Afroplacentalia/Xenarthra) and Boreoplacentalia served as the basis for estimating the times of placental divergences using paleontologically well-supported mammalian calibration points. These estimates placed the basal placental divergence between Boreoplacentalia and Notoplacentalia at approximately 102 MYA (million years ago). The current estimates of ordinal placental divergences are congruent with recent estimates based on nuclear data, but inconsistent with paleontological notions that have placed the origin of essentially all placental orders within an interval of 5-10 MY in the early Tertiary. Among less deep divergences the estimates placed the split between Gorilla and Pan/Homo at approximately 11.5 MYA and that between Pan and Homo at approximately 8 MYA. As a consequence of these estimates, which are in accord with recent progress in primate paleontology, the earliest divergences among recent humans become placed approximately 270,000 years ago, i.e. approximately 100,000 years earlier than the traditional age of "Mitochondrial Eve". Comparison between the two new mt genomes of Hylomys suillus (short-tailed gymnure) patently demonstrates the inconsistency that may exist between taxonomic designations and molecular difference, as the distance between these two supposedly conspecific genomes exceeds that of the three elephantid genera Elephas, Mammuthus and Loxodonta. In accordance with the progressive use of the term Placentalia for extant orders and extinct taxa falling within this group we forward new proposals for the names of some superordinal clades of placental mammals.

Mammalian mitogenomic relationships and the root of the eutherian tree.

The strict orthology of mitochondrial (mt) coding sequences has promoted their use in phylogenetic analyses at different levels. Here we present the results of a mitogenomic study (i.e., analysis based on the set of protein-coding genes from complete mt genomes) of 60 mammalian species. This number includes 11 new mt genomes. The sampling comprises all but one of the traditional eutherian orders. The previously unrepresented order Dermoptera (flying lemurs) fell within Primates as the sister group of Anthropoidea, making Primates paraphyletic. This relationship was strongly supported. Lipotyphla ("insectivores") split into three distinct lineages: Erinaceomorpha, Tenrecomorpha, and Soricomorpha. Erinaceomorpha was the basal eutherian lineage. Sirenia (dugong) and Macroscelidea (elephant shrew) fell within the African clade. Pholidota (pangolin) joined the Cetferungulata as the sister group of Carnivora. The analyses identified monophyletic Pinnipedia with Otariidae (sea lions, fur seals) and Odobenidae (walruses) as sister groups to the exclusion of Phocidae (true seals).