Factors influencing intraspecific variation and polymorphism in marine podocopid Ostracoda,with particular reference to Tertiary species from southeastern Australia

Work on intraspecific variation in ornate ostracods over the last 30 years is reviewed. Polymorphism (discontinuous variation) due to environmental and genetic factors (and combinations thereof) is discussed. Specimens of the ornate marine genera Cletocythereis, Hermanites, Notocarinovalva, Neobuntonia, Chapmanella, Actinocythereis, Spinobradleya and Loxoconcha, from Tertiary deposits of southeastern Australia, are examined for examples of significant intraspecific morphological variation. Variations in the degree of spinosity, the nature of spines, the degree and type of aggradation (celation), the occurrence of microreticulation, the shape of fossae, the form of eye tubercles and subcentral tubercles, combinations of reticulation and nodules, and the relationships between punctation, reticulation and spinosity, are described and illustrated. These variations are considered in relation to location, time, facies, inferred palaeoenvironment and assemblage. It is shown that the complex of factors connecting these variations with their expression by the phenotype does not allow their unqualified use in establishing palaeoecological parameters, especially where strict polymorphism is not established, or where the timescale of the variations may be several orders of magnitude out of step with the palaeoecological changes inferred from them. The necessity of high magnification illustrations is stressed. The entire range of research into intraspecific variation must be accessed if robust palaeoecological inferences are to be drawn.