Abstract
DR. W. A. CUNNINGTON, leader of the third Tanganyika Expedition (1904-5), has contributed to the Proceedings of the Zoological Society of London (December, 1920), a comparative study of the fauna of the African lakes—Tanganyika, Victoria Nyanza, Nyasa, Albert Nyanza, Edward Nyanza, and Kivu, with special reference to the first-named. The results of recent investigation, admirably summarised in this memoir, lend no support to the view put forward in 1898 by Mr. J. E. S. Moore, leader of the first and second expeditions, that Tanganyika represents an old Jurassic sea, and that its fauna is of relict nature. Of the six lakes, Tanganyika has by far the most remarkable fauna—of its 402 species 293 are endemic, and 57 of its 168 genera are peculiar to its waters; of the 146 species of fishes 121 are endemic, and a notable feature is the high degree of specialisation of the Cichlidæ, the lake presenting the richest known assemblage of this family. There is a large molluscan fauna, and of the species of gastropods more than two-thirds—the halolimnic forms (Moore)—exhibit a marine-like appearance, and these are, without exception, endemic. Noteworthy is the absence of Cladocera, and the relative scarcity of rotifers, which may be correlated with the salinity of the water, and especially with the excess of magnesium salts. Dr. Cunnington points out that geological investigation indicates that the extensive Beds of sandstone and conglomerate which occur in the lake regions were probably formed under fresh-water and terrestrial conditions, that the trough in which Tanganyika lies was apparently not formed until middle tertiary times, and that the lake had no outlet until recent geological times. Experts have not accepted Moore's comparison of shells from the lake with marine fossil shells of Jurassic age, or his views as to the primitive nature of the halolimnic gastropods. The endemic species in the fauna of Tanganyika are now held to be specialised rather than primitive. The conclusion reached is that Tanganyika owes its remarkable fauna to a long period of isolation, sufficiently extensive for the inhabitants of the lake to assume the characters of species and even genera distirict from those of the neighbouring parts of the continent.
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Fauna of African Lakes. Nature 109, 28 (1922). https://doi.org/10.1038/109028a0
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DOI: https://doi.org/10.1038/109028a0