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Prorastomidae is a 
''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 able to properly support its body weight while out of the water. However, several morphological features suggest that this species spent significant amounts of time in an aquatic environment, such as ''P. portellis pachyosteosclerotic ribs. Similar to an extant manatee's ribs, these ribs provided a ballast and allowed the animal to achieve neutral buoyancy. ''P. portelli'' lacked the large, muscular tail used in modern Sirenians to propel through the water column, and skeletal anatomy suggests that they instead garnered propulsive force through spinal undulations, similar to otters. This evidence suggests that ''P. portelli'' likely divided its time between terrestrial habitats and shallow aquatic habitats, convergently akin to hippopotamuses.
*'' Prorastomus''
The genus ''Prorastomus'' is also represented by only one known species. ''Prorastomus sirenoides'' lived in modern day Jamaica during the Mid Eocene, and it is thought to be the oldest Sirenian species discovered so far. Similar to ''P. portelli'', this quadrupedal Sirenian likely displayed a lifestyle comparable to hippos, spending large amounts of time both in and out of water. The species was determined to have had relatively large olfactory bulbs for a Sirenian, suggesting that the sense of smell was of importance to ''P. sirenoides'', and the trigenimal nerves, utilized in somatosensory, were found to be enlarged. Extant Sirenian species possess comparably large trigenimal nerves, allowing for highly sensitive facial tactility. Dentile fossils of ''P. sirenoides'' suggest that the species fed primarily on floating and emergent vegetation along its habitat.
family
Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...
of extinct sirenia
The Sirenia (), commonly referred to as sea-cows or sirenians, are an order of fully aquatic, herbivorous mammals that inhabit swamps, rivers, estuaries, marine wetlands, and coastal marine waters. The Sirenia currently comprise two distinct ...
ns from Jamaica
Jamaica (; ) is an island country situated in the Caribbean Sea. Spanning in area, it is the third-largest island of the Greater Antilles and the Caribbean (after Cuba and Hispaniola). Jamaica lies about south of Cuba, and west of Hispan ...
, related to the extant
Extant is the opposite of the word extinct. It may refer to:
* Extant hereditary titles
* Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English
* Extant taxon, a taxon which is not extinct, ...
manatee
Manatees (family Trichechidae, genus ''Trichechus'') are large, fully aquatic, mostly herbivorous marine mammals sometimes known as sea cows. There are three accepted living species of Trichechidae, representing three of the four living speci ...
s and dugong
The dugong (; ''Dugong dugon'') is a marine mammal. It is one of four living species of the order Sirenia, which also includes three species of manatees. It is the only living representative of the once-diverse family Dugongidae; its close ...
. 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 able to properly support its body weight while out of the water. However, several morphological features suggest that this species spent significant amounts of time in an aquatic environment, such as ''P. portellis pachyosteosclerotic ribs. Similar to an extant manatee's ribs, these ribs provided a ballast and allowed the animal to achieve neutral buoyancy. ''P. portelli'' lacked the large, muscular tail used in modern Sirenians to propel through the water column, and skeletal anatomy suggests that they instead garnered propulsive force through spinal undulations, similar to otters. This evidence suggests that ''P. portelli'' likely divided its time between terrestrial habitats and shallow aquatic habitats, convergently akin to hippopotamuses.
*'' Prorastomus''
The genus ''Prorastomus'' is also represented by only one known species. ''Prorastomus sirenoides'' lived in modern day Jamaica during the Mid Eocene, and it is thought to be the oldest Sirenian species discovered so far. Similar to ''P. portelli'', this quadrupedal Sirenian likely displayed a lifestyle comparable to hippos, spending large amounts of time both in and out of water. The species was determined to have had relatively large olfactory bulbs for a Sirenian, suggesting that the sense of smell was of importance to ''P. sirenoides'', and the trigenimal nerves, utilized in somatosensory, were found to be enlarged. Extant Sirenian species possess comparably large trigenimal nerves, allowing for highly sensitive facial tactility. Dentile fossils of ''P. sirenoides'' suggest that the species fed primarily on floating and emergent vegetation along its habitat.
See also
* Evolution of sireniansReferences
Eocene sirenians Prehistoric mammal families Eocene first appearances Eocene extinctions {{Paleo-sirenian-stub