Desmostylia

Desmostylia Temporal range: Oligocene-Miocene, 30.8–7.2 Ma PreЄ Є O S D C P T J K Pg N
Desmostylus, Royal Ontario Museum
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Infraclass:	Placentalia
Order:	†Desmostylia Reinhart 1959
Families and genera
Family †Desmostylidae Osborn 1905 †Behemotops Domning, Ray & McKenna 1986 †Desmostylus Marsh 1888 †Cornwallius Hay 1923 †Kronokotherium Pronina 1957 †Ounalashkastylus Chiba, Kentaro 2016 Family †Paleoparadoxiidae Reinhart 1959 †Ashoroa Inuzuka 2000 †Paleoparadoxia Reinhart 1959 †Neoparadoxia Barnes 2013

Desmostylia (from Greek δεσμά desma, "bundle", and στῦλος stylos, "pillar") is an extinct order of aquatic mammals that existed from the late Oligocene (Arikareean) to the late Miocene (Tortonian) (30.8 to 7.25 million years ago).

Desmostylians are the only known extinct order of marine mammals.

Desmostylia, together with Sirenia and Proboscidea (and possibly Embrithopoda), have traditionally been assigned to the afrotherian clade Tethytheria, a group named after the paleoocean Tethys around which they originally evolved. The relationship between Desmostylia and the other orders within Tethytheria has been disputed; if the common ancestor of all tethytheres was semiaquatic, the Proboscidea became secondarily terrestrial; alternatively, Desmostylia and Sirenia could have evolved independently into aquatic mammals. The assignment of Desmostylia to Afrotheria has always been problematic from a biogeographic standpoint, given that Africa was the locus of the early evolution of Afrotheria while Desmostylia has only been found along the Pacific Rim. That assignment has been seriously undermined by a 2014 cladistic analysis that places anthracobunids and desmostylians, two major groups of putative non-African afrotheres, close to each other within the laurasiatherian order Perissodactyla. However, a posterior study shows that, while anthracobunids are definite perissodactyls, desmostylians share the same amount of characters necessary for either Paenungulata or Perissodactyla, making their former assessment as afrotheres a possibility.