MORPHOLOGIC VARIATION IN TURONIAN TO MAASTRICHTIAN HETEROHELIX-GLOBULOSA (EHRENBERG)

Variables describing size and shape, ornamentation and proloculus char acteristics were measured on Heterohelix globulosa (Ehrenberg) populat ions in Turonian to Maastrichtian samples from a section near El Kef, Tunisia. Temporal variation is present in most variables. Test size an d strength of ornamentation show time-related trends, which, however, are not unidirectional. Maximum test length was found in Lower Maastri chtian samples. The most heavily ornamented tests are found in Santoni an and in Maastrichtian samples. Variation is continuous within a sing le sample and does not allow for quantitative recognition of distinct subpopulations. Globular morphotypes that were described as distinct s pecies, e.g. Heterohelix striata and H. reussi, fall within the range of variation and are interpreted as junior synonyms of one variable sp ecies, Heterohelix globulosa. The size of the proloculus showed an ove rall decrease from the Turonian to the Maastrichtian, with more rapid change during the Santonian. Number of chambers in the test and size o f the initial coil are inversely related to the proloculus diameter. N o biological explanation can be given for this trend, but it can be us ed for biostratigraphic dating in low diversity environments, since H. globulosa was a cosmopolitan species.