Desmostylia

Desmostylia is an extinct order of herbivorous aquatic mammals that lived around the North Pacific from the Oligocene to the Miocene. Its members had distinctive pillar-like teeth and unusually robust limbs.

Mammalia: Mammals are vertebrates distinguished by hair, mammary glands, and specialized middle-ear bones. Desmostylians were mammals whose unusual bodies evolved within this larger group.
Molar (tooth): A molar is a broad cheek tooth used mainly for crushing or grinding food. Desmostylian molars formed distinctive vertical pillars unlike those of most mammals.
Oligocene: The Oligocene is the geologic epoch spanning about 33.9 to 23 million years ago. The earliest known desmostylians appeared during this epoch.
Desmostylus: Desmostylus is a genus of extinct desmostylian mammals known from Miocene deposits around the North Pacific. Its name became the basis for the order, and its fossils display the group’s unusual teeth.
Mammalian phylogenetics: Mammalian phylogenetics reconstructs evolutionary relationships among living and extinct mammals. Different phylogenetic analyses place Desmostylia in competing parts of the mammal tree.
Afrotheria: Afrotheria is a mammalian clade that includes elephants, hyraxes, aardvarks, and several extinct groups. Some analyses place desmostylians among afrotherians, though their exact relationships remain unsettled.
Tooth enamel: Tooth enamel is the hard, mineralized outer covering of a tooth crown. Enamel preserved on desmostylian teeth helps reveal their structure and wear.
Miocene: The Miocene is the geologic epoch spanning about 23 to 5.3 million years ago. Desmostylia diversified and persisted through much of this epoch.
Paleoparadoxia: Paleoparadoxia is an extinct genus of desmostylian mammal known from Miocene deposits in the North Pacific region. Its fossils provide a well-known example of desmostylian anatomy.
Paleobiogeography: Paleobiogeography studies the geographic distribution of organisms through geological time. Its fossil range helps investigate how desmostylians spread around the North Pacific.

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PachyostosisBroader topic: Several desmostylians had unusually dense bones suited to shallow-water locomotion.