Definition
Paratheria is an obsolete taxonomic grouping that was once proposed for a set of mammals distinct from both marsupials (Metatheria) and placental mammals (Eutheria). The group primarily included the xenarthran mammals—sloths, anteaters, and armadillos—and occasionally other taxa such as pangolins and aardvarks.
Historical background
The term was introduced by British mammalogist Oldfield Thomas in 1887. In his review of tooth development among mammals, Thomas argued that the “edentates” (animals with reduced or absent teeth) exhibited unique dental characteristics that justified a separate subclass. He coined Paratheria from the Greek παρά (para, “beside”) to indicate a lineage positioned alongside but distinct from other major mammalian groups.
Thomas’s conception built on earlier ideas by Henri Marie Ducrotay de Blainville (1839), who had recognized edentates as a separate division, and Paul Gervais (1855), who suggested a distinct subclass for them. Subsequent researchers—including William Berryman Scott (1904) and William King Gregory (1910)—occasionally used the name Paratheria to refer to a superorder that encompassed xenarthrans together with other taxa such as pangolins (Pholidota), aardvarks (Tubulidentata), and certain extinct groups.
Taxonomic usage and decline
During the late 19th and early 20th centuries, Paratheria was employed in various classification schemes to group xenarthrans with other “edentate” mammals. However, the hypothesis received limited support. By the mid‑20th century, comparative anatomy and later molecular data demonstrated that xenarthrans are firmly placed within Placental mammals (Eutheria) and share closer affinities with other placental orders than with pangolins or aardvarks.
Interest in the Paratheria concept briefly resurfaced in the 1970s–1980s when newly discovered high‑crowned fossil teeth from Cretaceous and Paleogene deposits of Argentina were interpreted as potentially linking xenarthrans to other extinct groups (e.g., gondwanatheres). These ideas did not gain lasting acceptance, and modern mammalian systematics no longer recognize Paratheria as a valid taxon.
Current status
Today, Paratheria is regarded as a historical term of limited scientific relevance. Xenarthrans are classified within the order Xenarthra, itself part of the placental mammals (Eutheria). The former grouping that included pangolins and aardvarks has been abandoned in favor of separate orders (Pholidota, Tubulidentata) placed elsewhere within Eutheria based on robust phylogenetic evidence.
References
- Thomas, O. (1887). Review of tooth development in mammals. Proceedings of the Zoological Society of London.
- Gregory, W. K. (1910). Mammalian interrelationships. Bulletin of the American Museum of Natural History.
- Scott, W. B. (1904). Classification of Mammals. The American Naturalist.
- Gaudin, T., et al. (1996). Cretaceous and Paleogene mammalian teeth from Argentina. Journal of Vertebrate Paleontology.
Note: All information is drawn from the Wikipedia article “Paratheria (mammals)” and associated historical literature.
