Mammalia - Sirenia - Dugongidae

Alternative combination: Felsinotherium floridanum

Synonyms: Felsinotherium ossivallense Simpson 1932, Halitherium antiquum Leidy 1856, Halitherium antiquusm Leidy 1856, Ischyrosaurus antiquus Leidy 1856, Ischyrotherium antiquum Leidy 1856, Ischyrotherium antiquus Leidy 1856, Manatus antiquus Leidy 1856, Metaxytherium ossivalense Simpson 1932, Metaxytherium ossivallense Simpson 1932, Trichechus antiquus Leidy 1856

Full reference: O. P. Hay. 1922. Description of a new fossil sea cow from Florida, Metaxytherium floridanum. Proceedings of the United States National Museum 61(17):1-4

Belongs to Metaxytherium according to D. P. Domning 2008

Sister taxa: Metaxytherium aquitaniae, Metaxytherium arctodites, Metaxytherium crataegense, Metaxytherium krahuletzi, Metaxytherium lovisati, Metaxytherium medium, Metaxytherium riveroi, Metaxytherium serresii, Metaxytherium subapenninum

Type specimens:

• Metaxytherium floridanum: USNM 7221, a maxilla. Its type locality is Prairie Pebble Phosphate Co., which is in a Serravallian lagoonal sandstone in the Bone Valley Formation of Florida.
• Felsinotherium ossivallense: AMNH 26805.
• Manatus antiquus: Its type locality is between Moreau and Grand Rivers (USGS), which is in a Maastrichtian terrestrial horizon in the Lance Formation of South Dakota.

Ecology: aquatic herbivore