''Prorastomus sirenoides'' is an extinct species of primitive

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 ...

n that lived during the

Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', " ...

Epoch 40 million years ago in

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 His ...

Taxonomy

The generic name ''Prorastomus'', a combination of

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

(''prōra''), prow, and (''stoma''), mouth, refers to the lower jaw of the animal "resembling the prow of a

wherry A wherry is a type of boat that was traditionally used for carrying cargo or passengers on rivers and canals in England, and is particularly associated with the River Thames and the River Cam. They were also used on the Broadland rivers of No ...

". The

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

name ''Prorastomus'' comes from

''prora'' meaning "prow" and

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

''stomus'' meaning "mouth." In 1892, naturalist

Richard Lydekker Richard Lydekker (; 25 July 1849 – 16 April 1915) was an English naturalist, geologist and writer of numerous books on natural history. Biography Richard Lydekker was born at Tavistock Square in London. His father was Gerard Wolfe Lydekker, ...

respelled it as ''Prorastoma'' with a feminine ending, however this was unjustified as ''stomus'' is masculine in Latin. ''Prorastomus'' is one of two genera of the family

Prorastomidae 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 ...

, the other '' Pezosiren''. These two species are the oldest

ns, dating to the

. The first specimen was described by

paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

Sir Richard Owen Sir Richard Owen (20 July 1804 – 18 December 1892) was an English biologist, comparative anatomist and paleontologist. Owen is generally considered to have been an outstanding naturalist with a remarkable gift for interpreting fossils. Ow ...

in 1855, and, being found in Jamaica in the

Yellow Limestone Group The Yellow Limestone Group is a geologic group in Jamaica. It preserves fossils dating back to the Paleogene period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertain ...

, pointed to the origin of Sirenia as being in the New World rather than the Old World as was previously thought. However, the modern understanding of

Afrotheria Afrotheria ( from Latin ''Afro-'' "of Africa" + ''theria'' "wild beast") is a clade of mammals, the living members of which belong to groups that are either currently living in Africa or of African origin: golden moles, elephant shrews (also k ...

as a clade that originally diversified in Africa overturns this idea. The

holotype specimen A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

, BMNH 44897, comprises a skull, jaw, and

atlas An atlas is a collection of maps; it is typically a bundle of maps of Earth or of a region of Earth. Atlases have traditionally been bound into book form, but today many atlases are in multimedia formats. In addition to presenting geograp ...

of the neck vertebrae. When Owen first acquired the skull, it was broken in two between the eyes and the braincase. Another specimen was found in 1989 in the same formation, USNM 437769, comprising the

frontal bone The frontal bone is a bone in the human skull. The bone consists of two portions.'' Gray's Anatomy'' (1918) These are the vertically oriented squamous part, and the horizontally oriented orbital part, making up the bony part of the forehead, pa ...

, a tusk, vertebrae fragments, and ribs.

Description

While modern sirenians are fully aquatic, the ''Prorastomus'' was predominantly terrestrial, judging from the structure of its skull. Judging from its crown-shaped

molars The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone to ...

and the shape of its snout, it fed on soft plants. The snout is long, narrow, and, at the tip, bulbous. The nasal bones are larger than other sirenians. The nasal ridge is well developed, indicating it had a good sense of smell. The

s are smaller than usual for sirenians, though, as in other sirenians, it had a pronounced

brow ridge The brow ridge, or supraorbital ridge known as superciliary arch in medicine, is a bony ridge located above the eye sockets of all primates. In humans, the eyebrows are located on their lower margin. Structure The brow ridge is a nodule or crest ...

. Since ''Pezosiren'' has a sagittal crest, it is possible the ''Prorastomus'' specimen had one too before being eroded away.

References

*Barry Cox, Colin Harrison, R. J. G. Savage, and Brian Gardiner. (1999): The Simon & Schuster Encyclopedia of Dinosaurs and Prehistoric Creatures: A Visual Who's Who of Prehistoric Life.

Simon & Schuster Simon & Schuster () is an American publishing company and a subsidiary of Paramount Global. It was founded in New York City on January 2, 1924 by Richard L. Simon and M. Lincoln Schuster. As of 2016, Simon & Schuster was the third largest pu ...

. *David Norman. (2001): The Big Book Of Dinosaurs. Pg. 348, Welcome Books. *Richard Owen. (1855): On the fossil skull of a mammal (''Prorastomus sirenoïdes'', Owen) from the island of Jamaica. The Quarterly journal of the Geological Society of London, 11, pp. 541–543. Eocene mammals of North America Eocene sirenians Transitional fossils Prehistoric monotypic mammal genera Taxa named by Richard Owen Fossil taxa described in 1855 Paleogene Jamaica Fossils of Jamaica Prehistoric placental genera {{Paleo-sirenian-stub

Taxonomy

Description

See also

References