section_path: Natural history
section_name: Natural history
paragraph_text: Natural history
  
  The current course of the Congo River formed between 1.5 and 2 million years BP, during the Pleistocene. It is likely that during this period many upper tributaries of the Congo were captured from adjacent river basins, including the Uele and upper Ubangi from the Chari system and the Chambeshi River alongside a number of upper Kasai River tributaries from the Zambezi system.
  
  The Congo's formation may have led to the allopatric speciation of the bonobo and the common chimpanzee from their most recent common ancestor. The bonobo is endemic to the humid forests in the region, as are other iconic species like the Allen's swamp monkey, dryas monkey, aquatic genet, okapi, and Congo peafowl.
  
  In terms of aquatic life, the Congo River Basin has a very high species richness and among the highest known densities of endemics. As of 2009, almost 800 fish species have been recorded from the Congo River Basin (not counting Lake Tanganyika, which is connected but ecologically very different), and large sections remain virtually unstudied. For example, the section in Salonga National Park, which is about the size of Belgium, had still not been sampled at all in 2006. New fish species are scientifically described with some regularity from the Congo River Basin, and many undescribed species are known.
  
  The Congo has by far the highest diversity of any African river system; in comparison, the next richest are the Niger, Volta and Nile with about 240, 140 and 130 fish species, respectively. Because of the great ecological differences between the regions in the Congo basin—including habitats such as river rapids, deep rivers, swamps, and lakes—it is often divided into multiple ecoregions (instead of treating it as a single ecoregion). Among these ecoregions, the Livingstone Falls cataracts has more than 300 fish species, including approximately 80 endemics while the southwestern part (Kasai River basin) has more than 200 fish species, of which about a quarter are endemic.
  
  The dominant fish families—at least in parts of the river—are Cyprinidae (carp/cyprinids, such as Labeo simpsoni), Mormyridae (elephant fishes), Alestidae (African tetras), Mochokidae (squeaker catfishes), and Cichlidae (cichlids). Among the natives in the river is the huge, highly carnivorous giant tigerfish. Three of the more unusual endemics are the whitish (non- pigmented) and blind Lamprologus lethops, which is believed to live as deep as 160 metres (520 ft) below the surface, Heterochromis multidens, which is more closely related to cichlids of the Americas than other African cichlids, and Caecobarbus geertsii, the only known cavefish in Central Africa. There are also numerous endemic frogs and snails. Several hydroelectric dams are planned on the river, and these may lead to the extinction of many of the endemics.
  
  Several species of turtles and the slender-snouted, Nile and dwarf crocodile are native to the Congo River Basin. African manatees inhabit the lower parts of the river.