 Paratheria is an obsolete term for a taxonomic group including the xenarthran mammals ( sloths , anteaters , and armadillos ) and various groups thought to be related to them . It was proposed by Oldfield Thomas in 1887 to set apart the sloths , anteaters , armadillos , and pangolins , usually classified as placentals , from both marsupial and placental mammals , which were grouped together in the taxon Eutheria . The term was later applied to the Xenarthra as a whole, including the xenarthran mammals and the extinct Gondwanatheria . The term was used for the first time in 1887 by Oldfield Thomas