Xenotheria

Xenotheria is a proposed clade within Placentalia that has been used to describe a hypothetical grouping intended to unite Xenarthra (armadillos, sloths, anteaters) with Afrotheria (elephants, hyraxes, manatees, aardvarks, tenrecs, and related forms) as an early-diverging branch of placental mammals. The name derives from Greek xenos, meaning strange or foreign, and theria, meaning beasts.

The proposal emerged from comparative anatomy, with arguments pointing to shared features in jaw and dental morphology and certain ear-bone characteristics that some researchers interpreted as evidence for a common early placental ancestry preceding other major splits. However, the morphological signal is widely regarded as weak and contested, and Xenotheria has remained a controversial and debated concept. It gained visibility in some late 20th-century discussions but faced substantial criticism.

Fossil evidence attributed to Xenotheria is sparse and fragmentary. If such a clade existed, its last common ancestor would be placed in the Late Cretaceous to the Paleogene transition. In terms of distribution, a fully real Xenotheria would imply a broad, transcontinental reach, with modern descendants in the Americas (Xenarthra) and Africa (Afrotheria).

In contemporary systematics, Xenotheria is generally viewed as unsupported or obsolete. Most molecular phylogenetic analyses place Afrotheria and Xenarthra within larger frameworks such as Atlantogenata, or as early-diverging lineages within Placentalia, but not as a single, cohesive Xenotheria clade. The term persists mainly in historical accounts and discussions of alternative hypotheses about early mammal diversification.