Ammonoid Intraspecific Variability

Abstract

Two main types of intraspecific variation can be distinguished in ammonoids, which are not mutually exclusive: continuous and discontinuous variation. Although many authors acknowledge or implicitly assume a large intraspecific variability is possible in shell shape, ornamentation and suture line, it has only been rarely studied quantitatively. Several potential biases need to be taken into account when studying intraspecific variation of fossil populations including paleoecological, taphonomic and collection biases. Intraspecific variation might be controlled both by genetic and environmental parameters, although both are difficult to separate in fossil samples. In ammonoids, a large part of intraspecific variation in morphology and size has been attributed to differences in growth rates and development. Taking intraspecific variation properly into account is not only of prime importance for taxonomy, but also for studies on biostratigraphy, paleobiogeography, ecology, paleobiology and evolution of ammonoids.