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The Endemic Fish Fauna of Lake Lanao, and the Evolution of Higher Taxonomic Categories

George Sprague Myers
Evolution
Vol. 14, No. 3 (Sep., 1960), pp. 323-333
DOI: 10.2307/2405975
Stable URL: http://www.jstor.org/stable/2405975
Page Count: 11
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The Endemic Fish Fauna of Lake Lanao, and the Evolution of Higher Taxonomic Categories
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Abstract

1. The endemic fish fauna of Lake Lanao, all belonging to the family Cyprinidae, consisting of a species flock of 13 species and five species referred to four endemic genera, has evolved in a relatively short time, possibly as little as 10,000 years. 2. The distributional facts permit the identification, beyond reasonable doubt, of the single, still-existing, ancestral species that gave rise to the entire endemic fish fauna. 3. Certain specializations of the endemic Lanao genera are paralleled or approached by no others in the large, widespread family Cyprinidae; because they transcend the morphological limits of all non-Lanao cyprinids, these are termed supralimital specializations. 4. Supralimital specializations are shown to be very characteristic if not invariable features of all large, older, endemic lake-fish faunas; some are so distinctive as to provide characters worthy of family rank. 5. The stages of endemic lake-fish evolution are illustrated by examples, the youngest being the American Great Lakes, the oldest Lake Baikal. 6. A single preadapted fish family represented in the surrounding fluviatile fish fauna assumes dominance in the evolution of large endemic lake fish faunas. 7. The evolution of lake-fish faunas is compared to that of island faunas, and to the evolution of any groups newly admitted to extensive areas where competition is light or absent, and shown to be essentially similar in the relatively rapid production of supralimitally specialized forms. 8. The latter are often capable of becoming the founders of new genera, families, or perhaps even higher categories, at new adaptive levels. They have unquestionably already done so in the older lake-fish faunas, where certain endemic Tanganyika and Baikal genera are worthy of subfamilial or familial rank. 9. It is suggested that the origin of the excessively rich characid fauna of the Amazon River, and of the striking forms and groups of deep-sea fishes, has been due to similar tachytelic or quantum evolution. 10. It follows that opportunity for rapid radiative evolution is of very great importance in the evolution of higher categories, and that such opportunity still may occur from time to time through geological changes.

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