Spatiotemporal variation in morphological evolution in the Oligocene–Recent larger benthic foraminifera genus Cycloclypeus reveals geographically undersampled speciation

Accurate assessment of location and timing of speciation of species is needed to discriminate between macroevolutionary models explaining large scale biodiversity patterns. In this paper I evaluate fossil evidence of variation in geographical ranges through time, as well as spatio-temporal variation in morphological parameters to examine geographical aspects of speciation and range variation. Specifically I test for geographical morphological stability within time slices and for temporal modes of morphological change within lineages.

Past distribution ranges of all species of the large benthic foraminifera Cycloclypeus have been documented on paleogeographic maps. From those samples with sufficiently well preserved specimens internal morphological data were measured and analysed.

Within a small sample of six species in a single genus of reef associated large benthic foraminifera evidence for heterogeneity in geographic speciation modes, including vicariance, peripheral speciation, and sympatric speciation in the centre of the range has been found. Morphological evolution was found to be either homogeneous over large geographic ranges or spatially restricted. In time two gradually evolving lineages were found. Furthermore, an evolutionary transition of two species that previously was regarded as gradual, is shown to be punctuated with intermediate populations occurring restricted in both time and space.

I demonstrate the marked heterogeneity of evolutionary processes and the difficulty to make assumptions regarding tempo and mode of evolution. Furthermore, I introduce the concept of geographically undersampled punctuations. This example exposes some of the pitfalls when conclusions regarding the mode and location of speciation are based on the combination of phylogeny and extant distribution alone.