Some aspects of growth studies in fossils

Abstract

Growth studies are frequently of use in solving problems of taxonomy in fossils. As a by-product of such a study on the Permian brachiopod Dielasma elongata (Schloth.), the occur­ rence of sexual dimorphism in brachiopods is thought probable. Various problems involving limited growth and seasonal (incremental) growth are discussed; some possibilities in the study of trilobite ontogeny are indicated. Ma’s work on growth in corals has much significance in geological studies. A review of recent work on relative growth in fossil vertebrates allows distinction between different types of allomorphosis to be drawn, and some of the methods are criticized. The dwarfing of various mammals is indicated as a valuable future study. An interpretation of the evolution of Gryphaea is offered, which seems to afford an adaptive mechanism for a standard case of recapitulation and orthogenesis. Certain ‘katagenic’ trends in Graptoloidea and ammonites are interpreted as paedomorphic developments in forms of increasing potential size; the idea of a potential hypermorph is used. Finally, an analysis of growth in the skull of a labyrinthodont is used as a basis for discussion of changes in proportion in the evolution of major groups of vertebrates.