Article: Palaeobiology of Upper Cretaceous belemnites from the phosphatic chalk of the Anglo-Paris Basin
The phosphatic chalks of northern France exhibit a tripartite belemnite biostratigraphy, with Actinocamax veras Miller at their base. Gonioteuthis ex gr. quadrala in their upper portions, and G, quadrala Belemnitella praecursor Stolley at their summit. G.granulata (Blainville) is identified from isolated specimens collected from the base of the sequences; G. granulataquadrata (Stolley) is recognized within 'populations' from the summit of phosphatic chalks. Principal component factor analysis suggests that variation in guard morphology may be attributed to differences in guard size and to the evolutionary stage reached by individuals within the gradualistic series formed by the genus Gonioteuthis. Heterogeneity in one sample is the result of mixing of juvenile and mature populations caused by a catastrophic event, probably a storm. The presence of juveniles in all samples indicates a near-shore environment which was the normal habitat of belemnites. Hardgrounds show associated concentrations of belemnites because of greater food availability and their suitability as breeding sites.