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27-758: The Pindaré rises in the low hills which separate its basin from that of the Tocantins River to the south. In its lower reaches it is called the Pindaré-Mirim. It is a left tributary of the Mearim River , which it joins not far from that river's mouth in the Baía de São Marcos . The Serra do Tiracambu lies to the west, and separates the basin of the Pindaré from that of the Gurupí River . Part of

54-598: A connection with the Paraná and São Francisco rivers . The Tocantins and these two rivers flow in different directions, but all have their source in the Brazilian Plateau in a region where a low watershed allows some exchange between them. There are several fish species that migrate along the Tocantins to spawn, but this has been restricted by the dams. Following the construction of the massive Tucuruí Dam ,

81-420: A high richness of fish species, although it is relatively low by Amazon basin standards. More than 350 fish species have been registered, including more than 175 endemics . The most species rich families are Characidae (tetras and allies), Loricariidae (pleco catfish and allies) and Rivulidae (South American killifish). While most species essentially are of Amazonian origin, there are also some showing

108-515: A point about 160 km (99 mi) above its junction with the Tocantins, it saws its way across a rocky dyke for 20 km (12 mi) in roaring cataracts. Two other tributaries, called the Maranhão and Paranatinga , collect an immense volume of water from the highlands which surround them, especially on the south and south-east. Between the latter and the confluence with the Araguaia,

135-486: A prominent forehead and a much longer snout than those of most marine dolphins, as well as smaller eyes than marine dolphins. Because their aquatic environment is often turbid, their vision is not as well developed. River dolphins tend to be less active than marine dolphins. They feed mainly on fish, aided by echolocation . River dolphins have a complex set of acoustic calls that help shed light on their personalities, behaviors and interaction with other river dolphins. In

162-555: A study by Gabriel Melo-Santos et. Al they analyzed frequency contours of 727 signals They found that these signals had a critical similarity value of 96% and frequency contours were categorized into 237 sound-types. Interestingly the most notable and frequent sounds were emitted when calves were present shedding light on a close and complex mother child relationship. The findings show that the acoustic sounds of river dolphins are incredibly complex and are similar to those of by social delphinids, such as orcas and pilot whales. This species

189-596: A wider skull). It also differs from the Amazon and Bolivian river dolphins in the number of teeth per hemimandible (24–28 versus 25–29 and 31–35, respectively). However, I. araguaiaensis is still not recognized as a separate species by the Committee on Taxonomy of the Society for Marine Mammalogy , the largest international association of marine mammal scientists in the world. The Committee made these comments regarding

216-401: Is fragmented by six hydroelectric dams, so the population there is at particular risk. The authors of the discovery paper regard its probable eventual IUCN status to be Vulnerable or worse. The largest number of individuals of the new species is likely to occur in and around Cantão State Park , which contains most of the lakes in the Araguaia basin. However, commercial fishermen around

243-462: Is most closely related to the Amazon river dolphin ( Inia geoffrensis ), from which it is believed to have split about 2.08 million years ( Ma ) ago, on the basis of mitochondrial DNA sequence comparisons. The time of divergence corresponds to the time the Amazon and Araguaia-Tocantins river basins became separated, implying vicariant speciation. Major rapids in the lower Tocantins River (into which

270-528: Is a South American river dolphin population native to the Araguaia – Tocantins basin of Brazil . The recognition of I. araguaiaensis as a distinct species is still debated. It was originally distinguished from the Amazon river dolphin ( Inia geoffrensis ) in January 2014 on the basis of nuclear microsatellite and mitochondrial DNA data as well as differences in skull morphology (it generally has

297-672: Is the only known cave-adapted knifefish and one of only two known non-catfish in caves of the South American mainland (the other is the characid Stygichthys typhlops ). In its lower reaches, the Tocantins separates the Tocantins–Araguaia–Maranhão moist forests ecoregion to the east from the Xingu–Tocantins–Araguaia moist forests ecoregion to the west. It acts as a barrier that prevents dispersal of flora and fauna between these ecoregions. Downstream from

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324-664: The Araguaia River , has its extreme southern headwaters on the slopes of the Serra dos Caiapós . The Araguaia flows 1,670 km (1,040 mi) before its confluence with the Tocantins, to which it is almost equal in volume. Besides its main tributary, the Rio das Mortes , the Araguaia has twenty smaller branches, offering many miles of canoe navigation. In finding its way to the lowlands, it breaks frequently into waterfalls and rapids , or winds violently through rocky gorges, until, at

351-613: The Amazon proper. It flows through four Brazilian states ( Goiás , Tocantins , Maranhão , and Pará ) and gives its name to one of Brazil's newest states, formed in 1988 from what was until then the northern portion of Goiás . The Tocantins is one of the largest clearwater rivers in South America. It rises in the mountainous district known as the Pireneus , west of the Federal District, but its western tributary,

378-887: The Araguaia River flows) are thought to have contributed to isolating the two species, as the Pará River (into which the Tocantins flows) connects with the Amazon River . Inia araguaiaensis  (Araguaian river dolphin) Inia geoffrensis  ( Amazon river dolphin ) Inia boliviensis  ( Bolivian river dolphin ) Pontoporia blainvillei  ( La Plata dolphin ) † Lipotes vexillifer  ( baiji or Yangtse river dolphin) The estimated times of divergence with I. boliviensis , P. blainvillei and L. vexillifer are 2.9, 12.0 and 16.2 Ma ago, respectively. The total population of

405-518: The Araguaia confluence, in the state of Pará, the river used to have many cataracts and rapids, but they were flooded in the early 1980s by the artificial lake created by the Tucuruí Dam , one of the world's largest. When the second phase of the Tucuruí project was completed on November 30, 2010, a system of locks called Eclusas do Tucuruí was established with the goal of making a long extension of

432-407: The Tocantins is occasionally obstructed by rocky barriers which cross it almost at a right angle. The Tocantins basin (which includes the Araguaia River ) is the home of several large aquatic mammals such as Amazonian manatee , Araguaian river dolphin and tucuxi , and larger reptiles such as black caiman , spectacled caiman and yellow-spotted river turtle . The Tocantins River Basin has

459-581: The country. In the Tupi language , its name means " toucan 's beak" ( Tukã for "toucan" and Ti for "beak"). It runs from south to north for about 2,450 km (1,520 mi). While sometimes included in definitions of the Amazon basin, the Tocantins is not a branch of the Amazon River , since its waters flow into the Atlantic Ocean via an eastern channel of the Amazon Delta , alongside those of

486-479: The decision to not include I. araguaiaensis as an independent species: " Inia araguaiaensis , was described by Hrbek et al. (2014). However, this study only examined samples from two extremes of the distribution of Inia so is it unclear if the molecular differences observed represented real species-level separation or were due to sampling from two locations separated by a large distance. Diagnostic osteological differences were also reported. However, because this

513-597: The flow of the river changed. Some species have been adversely affected and there has been a substantial reduction in species richness in parts of the river. The São Domingos karst in the upper Tocantins basin is home to an unusually high number of cavefish species (more than any other region in the Americas): Ancistrus cryptophthalmus , several Ituglanis species, Pimelodella spelaea , Aspidoras mephisto , an undescribed Cetopsorhamdia species and Eigenmannia vicentespelaea . The last

540-465: The following specific discharge rates: Tocantins (11 L/s/km or 1.0 cu ft/s/sq mi), Araguaia (16 L/s/km or 1.5 cu ft/s/sq mi), Pará (17 L/s/km or 1.6 cu ft/s/sq mi) and Guamá (21 L/s/km or 1.9 cu ft/s/sq mi). Araguaian river dolphin The Araguaian river dolphin or Araguaian boto ( Inia araguaiaensis )

567-419: The margins of the great sandstone plateaus, from 300 to 600 metres (980 to 1,970 ft) elevation above sea-level, through which the rivers have eroded their deep beds. Around the estuary of the Tocantins the great plateau has disappeared, having been replaced by a part of the forest-covered, half submerged alluvial plain , which extends far to the north-east and west. The Pará River , generally called one of

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594-502: The mouths of the Amazon, is only the lower reach of the Tocantins. If any portion of the waters of the Amazon runs round the southern side of the large island of Marajó into the river Para, it is only through tortuous, natural canals, which are in no sense outflow channels of the Amazon. The Tocantins River records a mean discharge rate of 13,598 m /s (480,200 cu ft/s) and a specific discharge rate of 14.4 L/s/km (1.32 cu ft/s/sq mi). The sub-basins have

621-469: The river navigable. In total there are seven dams on the river ( Serra da Mesa dam , Cana Brava dam, São Salvador dam, Peixe Angical dam, Luiz Eduardo Magalhães (Lajeado) dam, Estreito dam, and Tucuruí dam), of which the largest are the Tucuruí and the Serra da Mesa dam. The flat, broad valleys, composed of sand and clay, of both the Tocantins and its Araguaia branch are overlooked by steep bluffs. They are

648-445: The river's basin lies in the 271,197 hectares (670,140 acres) Gurupi Biological Reserve , a full protected conservation unit created in 1988. Average annual rainfall is 2,169 millimetres (85.4 in). Temperatures range from 22 to 32 °C (72 to 90 °F) with an average of 27 °C (81 °F). The Pindaré basin is home to tropical moist broadleaf forest , and the river divides the Tocantins–Araguaia–Maranhão moist forests to

675-423: The species is estimated to be of the order of 600 to 1500 individuals, and genetic diversity is limited. The ecology of its habitat has been adversely affected by agricultural, ranching and industrial activities, as well as by the use of dams for hydroelectric power. The inhabited section of the Araguaia River probably extends over about 1500 km out of a total length of 2110 km. The Tocantins River habitat

702-523: The west from the Maranhão Babaçu forests to the east. This article related to a river in Maranhão , Brazil is a stub . You can help Misplaced Pages by expanding it . Tocantins River The Tocantins River (Portuguese: Rio Tocantins Portuguese pronunciation: [ˈʁi.u tokɐ̃ˈtʃĩs, tu-] , Parkatêjê : Pyti [pɨˈti]) is a river in Brazil , the central fluvial artery of

729-460: Was based on the examination of very few specimens (only 2 for the new species and only 9 for I. geoffrensis ), the authors’ conclusions are very concerning." Members of the genus are gray to pink in color and have a body length range from 1.53 to 2.6 m (5.0 to 8.5 ft). They have a dorsal ridge rather than a fin. Their neck vertebrae are unfused, allowing them to turn their heads sharply. Like other river dolphins, I. araguaiaensis has

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