High-level systematics of placental mammals: Current status of the problem

According to molecular data, the modern clades of placental mammals can be grouped into four supraordinal taxa (Xenarthra, Afrotheria, Euarchontoglires, and Laurasiatheria) whose phylogenetic interrelationships have been interpreted inconsistently. Among these taxa, the group Afrotheria has no morphological support. Within this group, there are orders that are clearly related to “condylarthrans” (“afroungulates”) and to insectivores (“afrosoricids”). The radiation of placental mammals (the crown clade Placentalia) started before the K/T boundary on the northern continents. Laurasiatheria are likely to be the oldest clade of placentals: the diversification of Lipotyphla and Euungulata started ∼80 Mya (Campanian) and ∼70 Mya (Maastrichtian), respectively. It is shown that the fossil record is the only reliable method to test the phylogenetic hypotheses based on the material of the molecular and morphological studies of recent taxa.