Prorastomidae is a

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

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 extant Sirenia comprise two distinct famili ...

ns from

Jamaica Jamaica is an island country in the Caribbean Sea and the West Indies. At , it is the third-largest island—after Cuba and Hispaniola—of the Greater Antilles and the Caribbean. Jamaica lies about south of Cuba, west of Hispaniola (the is ...

, related to the

extant Extant or Least-concern species, least concern 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 * Exta ...

manatee Manatees (, family (biology), family Trichechidae, genus ''Trichechus'') are large, fully aquatic, mostly herbivory, herbivorous marine mammals sometimes known as sea cows. There are three accepted living species of Trichechidae, representing t ...

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 closest ...

. The family includes the oldest known fossils of Sirenians, represented in two genera: *''

Pezosiren ''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 ...

'' ''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 ''Prorastomus sirenoides'' is an extinct species of primitive sirenian that lived during the Eocene Epoch 40 million years ago in Jamaica. Taxonomy The generic name ''Prorastomus'', a combination of Greek (''prōra''), prow, and (''stoma''), m ...

'' 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 trigeminal nerves, utilized in somatosensory, were found to be enlarged. Extant Sirenian species possess comparably large trigeminal 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.

References

Eocene sirenians Prehistoric mammal families Eocene first appearances Eocene extinctions {{Paleo-sirenian-stub

See also

References