Hohenegger. Johann 1978 07 15: Populationsgenetische Deutung des morphologischen Wandels der triassischen Foraminifere Nodosaria striatoclavata. [A population genetic interpretation of the morphological transformation ofTriassic foraminifer Nodosaria striatoclavata.]Lethaia, Vol. 11, pp. 199–215. Oslo. ISSN 0024–1164.
In Middle Triassic (Ladinian) basin areas immediately adjacent to reefs, Nodosaria striatoeclavata Spandel exhibits during the early Ladinian a morphological transformation in the direction of the simultaneously occurring Nodosaria liratella Tappan. Statistical confirmation of this trend is provided by such parameters as growth in test breadth and degree of bulging of the penultimate chamber. The ribbing, too, shows a directed change. There are three possible explanations for this morphological manifestation of a fusion of two species from a population genetic viewpoint: (1) Phyletic evolution of Nodosaria striatoclavata with ‘convergence’ towards Nodosaria liratella. (2) Recurrent appearance of species which evolved rapidly from a single line of origin (‘punctuated equilibrium’). (3) Fusion of species through successive introgression of genes after the collapse of isolation.