Abstract

Assemblages of diminutive brachiopods may result from any one or any combination of the following factors: (1) actual dwarfing due to physiological retardation of growth, (2) accumulations of immature specimens of normally larger species and adults of smaller species due to segregation by moving water, and (3) accumulation of immature specimens because of environmental factors tending to produce subnormal fife-span or exceptionally high mortality of the younger shells. Interpretation in any given instance is a matter of determining from the shells themselves, from careful comparison with recognizably normal assemblages of near homotaxial equivalence, and from the physical and chemical nature of the entombing sediments which factor or combination of factors is the more logical. The paleoecological significance of assemblages of diminutive brachiopods as such is thus indirect. They merely bring attention to a situation the interpretation of which depends on a variety of physical, chemical, and biological considerations. The brachiopod faunas of the "Tully pyrite," the "Clinton hematite," the Glen Park and Salem limestones, and the Windsor series are briefly discussed. The fact emerges that more data are needed on the ecology of recent brachiopods and on assemblages of diminutive fossils and their entombing sediments.

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