Desmostylia Temporal range: Oligocene-Miocene, 30.8–7.2 Ma |
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Desmostylus, Royal Ontario Museum | |
Scientific classification | |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Mammalia |
Infraclass: | Placentalia |
Order: |
†Desmostylia Reinhart 1959 |
Families and genera | |
The Desmostylia (from Greek δεσμά desma, "bundle", and στῦλος stylos, "pillar") are 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.
The 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 the Desmostylia and the other orders within the Tethytheria has been disputed; if the common ancestor of all tethytheres was semiaquatic, the Proboscidea became secondarily terrestrial; alternatively, the 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 the Afrotheria while the Desmostylia have 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.