This is a study of size- and shape-variation in a sampled sequence of Late Santonian Veeniafawwarensis Honigstein and Oertliella cretaria (van den Bold). The material was obtained from limestone in a roadworks quarry at Shiloah, Israel. The main source of variation is ecophenotypic which seems to be connected with the magnesium content of the palaeo-environment; it is expressed by the development of spinosity. There is also ornamental variation between the contrasting poles of smoothness and bulbosity. A second source of variation is intrinsic (genetic) and is not under open ecological control; it leads to permanent, minute structural modifications in shape and in the disposition of the ventrolateral ornament. Essentially the same ecophenotypic responses were recognized in both species. About two thirds of the observed shape-history of these species is shared. In addition to the multivariate statistical methods of canonical variates and principal components, the geometrical method of shape-coordinates was used. Palaeoecological interpretations are supported by geochemical analyses and the analysis of the foraminiferal content of the sediments.
- ecophenotypic variation