Afrotheria is now recognized as one of the three major groups within the Eutheria (containing placental mammals). Relations within the three cohorts, Afrotheria, Xenarthra, Boreoeutheria, and the identity of the placental root, remain somewhat controversial. Afrotheria as a clade has usually been discussed without a Linnaean rank, but has been assigned the rank of cohort, magnorder, and superorder. One reconstruction, which applies the molecular clock, proposes that the oldest split occurred between Afrotheria and the other three some 105 million years ago in the mid-Cretaceous, when the African continent was separated from other major land masses. This idea is consistent with the fossil record of Xenarthra, which is restricted to South America (following recent consensus that "Eurotamandua" is not a xenarthran). However, Afrotheria itself does not have a fossil record restricted to Africa, and appears in fact to have evolved in the continent's isolation. More recent, genomic-scale phylogenies favor the hypothesis that Afrotheria and Xenarthra comprise sister taxa at the base of the placental mammal radiation, suggesting an ancient Gondwanan clade of placental mammals. Relations between the various afrotherian orders are still being studied. On the basis of molecular studies, elephants and manatees appear to be related, and likewise elephant shrews and aardvarks. These findings are compatible with the work of earlier anatomists. Many extant members of Afrotheria appear to have a high risk of extinction (perhaps related to the large size of many). Species loss within this already small group would comprise a particularly great loss of genetic and evolutionary diversity. The IUCN Afrotheria Specialist Group notes that Afrotheria, as currently reconstructed, includes nearly a third of all mammalian orders currently found in Africa and Madagascar, but only 75 of more than 1,200 mammalian species in those areas. While most extant species assigned to Afrotheria live in Africa, some (such as the Indian elephant and three of the four sirenian species) occur elsewhere; many of these are also endangered. Prior to the Quaternary extinction event, proboscideans were present on every continent of the world except Australia and Antarctica. Hyraxes lived in much of Eurasia as recently as the end of the Pliocene. The extinct afrotherian orders of embrithopods and desmostylians were also once widely distributed.