THE STRUCTURE OF INDIVIDUAL VARIATION IN MIOCENE GLOBOROTALIA.

Analysis of probability distributions of individual organisms provides a common language to describe synchronic and diachronic diversity. When based on an appropriate quantitative description of morphology, this language can be used to explore the temporal component of diversity embedded in the fossil record. Miocene Globorotalia (planktonic foraminifera) from Deep Sea Drilling Project site 593 are described using two-point registration of landmarks in two views (spiral and apertural) and medial-axis analysis of the shape of the final chamber. The equiangular spiral parameters Θ (the angle of increment), r (the expansion rate), and t (the rate of translation down the spiral axis) appear as principal components of the landmark data. Chamber shape variation is described by three principal components of medial-axis curvature. Partial-least-squares analysis demonstrates that the first components of within-morphospace variation also explain the patterns of correlation between the landmark and chamber-shape morphospaces. In the landmark morphospaces, the distribution of sampled individuals is continuous and roughly elliptical with few stratigraphic changes. In the chamber-shape morphospace, the distribution is continuous but shows complex features beyond the elliptical; the occupied morphospace changes stratigraphically, but neither strict cladogenesis nor strict anagenesis explains the derivation of new morphologies. Exemplars of named morphospecies are scattered across these spaces with continuous variation among all forms. These names cannot be assumed to represent discrete entities. © 1990 The Society for the Study of Evolution.