Metaxytherium

Metaxytherium (Metaxytherium (De Christol 1840))

Order: Sirenia

Family: Dugongidae

Time period: Late Oligocene-Late Pliocene (~25.7–3 Ma, Paratethys, Mediterranean, Caribbean Sea and Pacific coastline.) 

Size: 3-5 m in length, 250-1000 kg of weight

Metaxytherium is an extinct genus of dugong that lived from the Oligocene until the end of the Pliocene. The name Metaxytherium means "inbetween beast" or "intermediate beast". The name derives from the original interpretation of it being an intermediate form between dugongs and manatees. Fossil remains have been found in Africa, Europe, North America and South America. Generally marine seagrass specialists, Metaxytherium inhabited the warm and shallow waters of the Paratethys, Mediterranean, Caribbean Sea and Pacific coastline. American species of this dugong are considered to be ancestral to the North Pacific family Hydrodamalinae, which includes the giant Steller's sea cow.

There are several genera that are now synonymous with Metaxytherium, including Thalattosiren, Halianassa, Felsinoitherium, Cheirotherium and Hesperosiren. Several species previously considered distinct have likewise been synonymized with already established Metaxytherium species.

Unlike modern sirenians, Metaxytherium is known from a multitude of environments that it shared with other species of sea cows.