''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 speci ...

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 and US customary systems. It is traditionally defined as the area of one chain by one furlong (66 by 660 feet), which is exactly equal to 10 square chains, of a square mile, 4,840 square ...

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 teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

, where the buccinator 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 teeth in place. The mandible sits beneath the maxilla. It is the only movable bon ...

, 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 ...

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, in

Nova Mamoré Nova Mamoré is a municipality located in the Brazilian state of Rondônia. In 2020, the population of Nova Mamoré was 31,392. Its area is 10,072 km². Economy The economy of Nova Mamoré is based on mainly agriculture and wood. Its main agr ...

, 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 Pampatheriidae ("Pampas beasts") is an extinct family of large plantigrade armored armadillos related to extant armadillos in the order Cingulata. However, pampatheriids have existed as a separate lineage since at least the middle Eocene Musters ...

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 inh ...

. 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 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 finally confirmed ...

, 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