Resolution of the Early Placental Mammal Radiation Using Bayesian Phylogenetics

TLDR

Molecular phylogenetic studies have resolved placental mammals into four major groups, but the full interordinal hierarchy, including the root position, remains unclear, which is essential for early biogeographic history. We used Bayesian and maximum‑likelihood analyses on a 16.4‑kb molecular dataset to infer placental phylogeny. The interordinal relationships are largely resolved, with the basal split between Afrotheria and other placentals at ~103 Ma, possibly reflecting the Cretaceous separation of South America and Africa, and suggesting a Southern Hemisphere origin for crown‑group Eutheria.

Abstract

Molecular phylogenetic studies have resolved placental mammals into four major groups, but have not established the full hierarchy of interordinal relationships, including the position of the root. The latter is critical for understanding the early biogeographic history of placentals. We investigated placental phylogeny using Bayesian and maximum-likelihood methods and a 16.4-kilobase molecular data set. Interordinal relationships are almost entirely resolved. The basal split is between Afrotheria and other placentals, at about 103 million years, and may be accounted for by the separation of South America and Africa in the Cretaceous. Crown-group Eutheria may have their most recent common ancestry in the Southern Hemisphere (Gondwana).