''Trichechus hesperamazonicus'', the western Amazonian manatee, is an extinct species of

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 species ...

that lived about 40 thousand years ago in the

Madeira River The Madeira River ( pt, Rio Madeira, link=no ) is a major waterway in South America. It is estimated to be in length, while the Madeira-Mamoré is estimated near or in length depending on the measuring party and their methods. The Madeira is ...

, in the Brazilian state of Rondonia. It is known from this single locality, with possible occurrences in the Brazilian state of

Acre The acre is a unit of land area used in the imperial Imperial is that which relates to an empire, emperor, or imperialism. Imperial or The Imperial may also refer to: Places United States * Imperial, California * Imperial, Missouri * Imp ...

Description

''Trichechus hesperamazonicus'' is known by two fragmentary mandibles and part of the palate. Compared with other manatees, it has a wide space between the posterior lower tooth row and ascending ramus of

dentary In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...

, where the

buccinator The buccinator () is a thin quadrilateral muscle occupying the interval between the maxilla and the mandible at the side of the face. It forms the anterior part of the cheek or the lateral wall of the oral cavity.Illustrated Anatomy of the Head ...

muscle is located, and a wide ascending ramus of the

mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...

, which covers the posterior end of the tooth row. It also shares some characteristics with living species, as relatively few large teeth and few mental foramina as '' T. manatus'' and '' T. senegalensis'' (in contrast with the many smaller teeth and many mental foramina of '' T. inunguis'') and a straight and shallow mandibular symphysis as '' T. inunguis'' and '' T. senegalensis'' (in contrast with the downturned snout and deep mandibular symphysis of '' T. manatus''). The affinities of this species are still not fully resolved, being recovered in a polytomy with '' T. inunguis'' and a clade formed by '' T. manatus'' and '' T. senegalensis''

Distribution

The

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 ...

name ''hesperamazonicus'' refers to the western localization of the species, ''hesperos'' (west) and ''amazonicus'' (from the Amazon region). The fossil was found near the village of

Araras Araras () is a municipality located in the interior of State of São Paulo, Brazil. The population is 135,506 as of the 2020 IBGE estimate. Etymology Araras means macaws. Sports União São João Esporte Clube, founded in 1981, is the most suc ...

, in Nova Mamoré, state of Rondonia,

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

. The site also yielded pampatheres and a fossil species of

tapir Tapirs ( ) are large, herbivorous mammals belonging to the family Tapiridae. They are similar in shape to a pig, with a short, prehensile nose trunk. Tapirs inhabit jungle and forest regions of South and Central America, with one species inhabit ...

. ¹⁴C dates from associated wood samples give an age of 44,710 ± 880 years before present. At that time, the

had slow currents and many marginal lakes. At the end of the

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

, changes on the river regime originated several

rapids Rapids are sections of a river where the river bed has a relatively steep gradient, causing an increase in water velocity and turbulence. Rapids are hydrological features between a ''run'' (a smoothly flowing part of a stream) and a ''cascade''. ...

, creating an environment unsuitable to manatees, that are currently absent from the region.

References

{{Taxonbar, from=Q96057722 Sirenians Fossil taxa described in 2020 Prehistoric mammals