Fransızca adı: Jean Louis Rodolphe Agassiz)(1807-73)

Louis John Rudolph Agassiz
İsviçre asıllı, ABD'li doğabilimci ve jeolog. Harvard Kıyaslamalı Anatomi Müzesi kurucusu. Bilimsel eserleri, özellikle balık fosilleri ile ilgili çalışmaları yansıttı. Bu alanda, yaklaşık 1000 tür hakkında ayrıntılı bilgi verdi.

Agassiz soon found that his palaeontological labours rendered a new basis of ichthyological absolutely necessary. The fossils rarely exhibited any traces of the soft tissues of fishes. They chiefly consisted of the teeth, scales, and fins, even the bones being perfectly preserved in but comparatively few instances. Hence the classifications of Cuvier and other naturalists were of little use to him in determining the mutual relations of the fossil forms. He therefore adopted his well-known classification, which divided fishes into four groups - viz., Ganoids, Placoids, Cycloids, and Ctenoids. The first of these groups was chiefly represented amongst living fishes by the Peidosteus or bony pike of the great American rivers; by the Polypterus or Bischir of the Nile; and by the sturgeon. The last fish has a wide geographical range; but the other two, which best display the characters on which Agassiz based his Ganoid class, are limited to the fresh-water rivers of local geographical areas. But in the Palaeozoic and Mesozoic ages it was strikingly otherwise. The Ganoids were the most remarkable as well as the most widely diffused of primeval fishes; we find them equally in the fresh-water deposits of the weald, in the marine deposits of the oolites, the chalk, and the magnesian limestone, and in the most mixed and dubious deposits of the coal measures. Agassiz, therefore, was fully justified in attaching very great importance to this hitherto unrecognized class. Indeed, later ichthyologists - e.g., J. Muller and Professor Owen - have found it necessary to retain the class in their recent classifications, though in a modified form. The remaining portions of Agassiz' system have not been adopted by them; but though they do not accept the terms Placoids, Cycloids, and Ctenoids as presenting classes, all zoologists employ them as new and convenient adjectives, of the utmost value to students of systematic ichthyology. One reason for the rejection of Agassiz' system by modern ichthyologists is the obvious one that he draws the characteristics of his classes from a single organ-the skin-and that not the most important. At the same time, it must be admitted that the Placoids, like the Ganoids, also constituted a natural group closely corresponding with the Pisces cartilaginei of Cuvier and others. The distinction between Cycloids and Ctenoids was a much more trivial one, and needlessly separated closely-allied forms. It is only those who are familiar with the magnitude and difficulties of the task thus undertaken that can appreciate the daring courage of the youth who grappled with it. Under twenty-five years of age, and, as already observed, with limited financial resources, he nevertheless seems to have known no fear. He soon announced to geologists several important generalizations, the correctness of which has been confirmed by all subsequent research. In particular, he pointed out that no examples of cycloids and Ctenoids, comprehending the bulk of the fishes now seen in our markets, where to found in rocks of older date than the cretaceous age.

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