Evolution and homeomorphy in the development of the Paleocene Planorotalites pseudomenardii and the Miocene Globorotalia (Globorotalia) margaritae lineages

The Paleocene Subbotina pseudobulloides lineage is shown to evolve gradually through the intermediate species Planorotalites compressa and Planorotalites ehrenbergi to Planorotalites pseudomenardii and Planorotalites troelseni. The latter two forms are found to be endmembers in a morphological continuum, and the transitional ancestry of the lineage is found to contain no statistically definable cladogenetic event. Rates of evolution calculated for the lineage on the basis of different variables are slow and relatively invariant when compared to other foraminiferal lineages. Planorotalites pseudomenardii was compared to its Neogene "homeomorph", Globorotalia margaritae and found to be readily distinguished by discriminant analysis, and biometric evidence suggests that G. margaritae is derived from G. scitula.