''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 extant Sirenia comprise two distinct famili ...

n that lived during the

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

Epoch 40 million years ago in

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 ...

Taxonomy

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

Greek Greek may refer to: 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 of all kno ...

(''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 (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

name ''Prorastomus'' comes from

''prora'' meaning "prow" and

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

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

naturalist Natural history is a domain of inquiry involving organisms, including animals, fungi, and plants, in their natural environment, leaning more towards observational than experimental methods of study. A person who studies natural history is cal ...

Richard Lydekker Richard Lydekker (; 25 July 1849 – 16 April 1915) was a British naturalist, geologist and writer of numerous books on natural history. He was known for his contributions to zoology, paleontology, and biogeography. He worked extensively in cata ...

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

genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...

of the family

Prorastomidae Prorastomidae is a Family (biology), family of Extinction, extinct sirenians from Jamaica, related to the Extant taxon, extant manatees and dugong. The family includes the oldest known fossils of Sirenians, represented in two genera: *''Pezosiren ...

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

ns, dating to the

. The first specimen was described by

paleontologist Paleontology, also spelled as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure geolo ...

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

in 1855, and, being found in Jamaica in the Yellow Limestone Group, 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 superorder of placental mammals, the living members of which belong to groups that are either currently living in Africa or of African origin: golden moles, elephan ...

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

holotype specimen A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was Species description, formally described. It is either the single such physical example (or illus ...

, BMNH 44897, comprises a skull, jaw, and

atlas An atlas is a collection of maps; it is typically a bundle of world map, maps of Earth or of a continent or region of Earth. Advances in astronomy have also resulted in atlases of the celestial sphere or of other planets. Atlases have traditio ...

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 In the human skull, the frontal bone or sincipital bone is an unpaired bone which consists of two portions.'' Gray's Anatomy'' (1918) These are the vertically oriented squamous part, and the horizontally oriented orbital part, making up the bo ...

, a tusk, vertebrae fragments, and

rib In vertebrate anatomy, ribs () are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the thoracic cavity, enabling the lungs to expand and thus facilitate breathing by expanding the ...

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 tooth, teeth at the back of the mouth. They are more developed in mammal, mammals. They are used primarily to comminution, grind food during mastication, chewing. The name ''molar'' derives from Latin, '' ...

and the shape of its snout, it fed on soft plants. The snout is long, narrow, and, at the tip, bulbous. The

nasal bone The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face and by their junction, form the bridge of the upper one third of the nose. Eac ...

s 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 and some other animals. In humans, the eyebrows are located on their lower margin. Structure The brow ri ...

. Since ''Pezosiren'' has a

sagittal crest A sagittal crest is a ridge of bone running lengthwise along the midline of the top of the skull (at the sagittal suture) of many mammalian and reptilian skulls, among others. The presence of this ridge of bone indicates that there are excepti ...

, 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 LLC (, ) is an American publishing house owned by Kohlberg Kravis Roberts since 2023. It was founded in New York City in 1924, by Richard L. Simon and M. Lincoln Schuster. Along with Penguin Random House, Hachette Book Group US ...

. *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 Monotypic prehistoric placental genera Taxa named by Richard Owen Fossil taxa described in 1855 Paleogene Jamaica Fossils of Jamaica {{Paleo-sirenian-stub

Taxonomy

Description

See also

References