CHARACTERISTICS OF PELAGIC AND BOTTOM LIFE 329 



the characteristic abyssal fauna reflects the particular ocean's 

 history and the faunal development in the surface layers, because 

 it has a slower evolutionary development in comparison with the 

 shallow-water fauna. This explains the presence of old and primi- 

 tive forms. 



Our present knowledge of the taxonomy and distribution of the 

 oceanic flora and fauna, more especially the pelagic fauna, makes 

 it possible to focus attention on their significance in suggesting the 

 permanent character or at least on the great antiquity of the 

 oceanic trenches themselves. However, some preliminary assump- 

 tions must be made: (1) the paleontologists thus far know nothing 

 of the pelagic sediments; (2) the taxonomic differentiation of fauna 

 in various parts of the ocean should furnish evidence indicating 

 the age of the local differentiation; (3) the pelagic fauna Is charac- 

 teristically of great antiquity. If these assumptions are true, it is 

 obvious that the difference today between the surface and deep- 

 water faunas in the Atlantic and Pacific oceans, as well as the 

 availability of the pelagic fauna, requires the further assumption 

 that the oceanic depths are permanent. This is incompatible with 

 the idea of a local discontinuity in these depths. If this were the 

 case, the vertical and horizontal isolation of the faunal types would 

 not be shown — the oceanic fauna would inevitably be more 

 homogeneous, and the endemic fauna would not have become 

 individualized in separate parts of the world ocean. 



At present, one more picturesque chapter in oceanic history is 

 being unfolded. Our knowledge in this field is insufificient even in 

 shallow-water zones. The statement made at the last meeting of 

 the Special Committee on Oceanic Research (SCOR) in September 

 1958 was true: "Except in a few cases it is not possible to assess 

 the sizes of marine populations at different trophic levels, or the 

 biological productivity on a worldwide basis. Quantitative data 

 are absent or inadequate in many regions, while in others inter- 

 calibration of collecting and assay methods is necessary." One 

 cannot disagree with Thorson's (1958, p. 68) statement that "the 

 first stage . . . must be a thorough quantitative mapping of the 

 level-bottom communities" and that "very little work has so far 

 been done in the United States." 



