Eocene sirenians

Prorastomus sirenoides is an extinct species of primitive sirenian that lived during the Eocene Epoch 40 million years ago in Jamaica.

thumb|Pezosiren portelli cast skeleton Prorastomidae is a family of extinct sirenians from Jamaica, related to the extant manatees and dugong. The family includes the oldest known fossils of Sirenians, represented in two genera: Pezosiren Pezosiren comprises one known species, Pezosiren portelli, that was discovered in modern-day Jamaica. One of the earliest true Sirenian species, P. portelli is distinct from extant Sirenians due to its quadrupedal stature. The species is estimated to have lived 50 million years ago during the Mid Eocene, and the skeletal elements suggest that P. portelli was

Pezosiren portelli, also known as the "walking manatee", is a basal sirenian from the early Eocene of Jamaica, 50 million years ago. The type specimen is represented by a Jamaican fossil skeleton, described in 2001 by Daryl Domning, a marine mammal paleontologist at Howard University in Washington, DC. It is believed to have had a hippopotamus-like amphibious lifestyle, and is considered a transitional form between land and sea mammals.

left|thumb|Drawing of skeleton Protosiren is an extinct early genus of the order Sirenia. Protosiren existed throughout the Lutetian to Priabonian stages of the Middle Eocene. Fossils have been found in the far-flung locations like the United States (South Carolina, North Carolina and Florida), Africa (Egypt), Europe (France, Germany and Hungary) and Asia (India and Pakistan).

Halitherium is a dubious genus of extinct dugongid sea cow that arose in the late Eocene, then became extinct during the early Oligocene. Its fossils are common in European shales. Inside its flippers were finger bones that did not stick out. Halitherium also had the remnants of back legs, which did not show externally. However, it did have a basic femur, joined to a reduced pelvis. Halitherium also had elongated ribs, presumably to increase lung capacity to provide fine control of buoyancy.

Protosirenidae is an extinct primitive family of the order Sirenia.

left|thumb|Drawing of skeleton. left|thumb|E. libyca and an extant manatee by Charles R. Knight, 1907 left|thumb|Size of Eosiren (purple) compared to other Eocene sirenians and a human. Eosiren is an extinct genus of sea cow that lived during the Late Eocene (later Priabonian) to Early Oligocene (Rupelian). Several fossils have been found in Egypt. It seems like the species E. abeli were contemporaneous with Protosiren and Eotheroides. Like them, Eosiren closely resembled modern sirenians, with the primary differences being somewhat larger innominates and the presence of thigh bones.

Prototherium is a genus of extinct sirenian related to the dugong. It is known from middle (Bartonian) and upper Eocene deposits in Italy and Spain. Type species is P. veronenses (Zigno, 1887) thumb|left|P. veronense skull Three species are now included in the genus, but their phylogenetic relations are not resolved and possibly one of them Prototherium intermedium Bizzotto 1983 must be excluded. In the same way, relations between Prototherium and other genus are confused and need revision. A third species was described in Spain in 2016, P.ausetanum.

Sobrarbesiren (meaning "siren from Sobrarbe") is a genus of extinct sirenian that lived in the Eocene, about 47 million years ago. The type and only species is S. cardieli, known from a multitude of specimens from the Spanish Pyrenees. Sobrarbesiren was a medium-sized animal, long and still retaining both pairs of limbs. Although initially thought to be amphibious, later studies instead suggest that they would have been fully aquatic and been selective sea grass browsers. Unlike modern dugongs and manatees, they likely lacked a tail fluke, although it would have appeared horizontally flattened

Eotheroides is an extinct genus of Eocene sirenian. It is an early member of the family Dugongidae, which includes the extant dugong. Fossils have been found from Egypt, India, and Madagascar. Eotheroides was first described by Richard Owen in 1875 under the name Eotherium, which was replaced by the current name in 1899.