Cerithium giganteum (= Campanile giganteum) (†) is a portentous marine gastropod, a snail with a narrow, conical shell that is found as a fossil in two layers of the member Tossa from the geological formation Santa Maria, in the counties of Bages and Moianès.
Cerithium giganteum (†) has an acute shell up to cm long by 18 cm wide made of maximum 22 turns. The opening is large and eccentric, biased from the axis of the shell. The shell is beautiful with tips growing from the vertex to the base, almost absent in the first turns and obvious in the last one. The shell inside is smooth.
Fossils of Cerithium giganteum (†) can be from the shell with its ornamentations more or less preserved or, more often, from its internal mould that is released after the external part is fully eroded. The internal mould displays the smooth coils, like the turns of a spiral staircase with perfect helical geometry. Complete and well preserved fossils of this size are very rare. On the other hand, partial fossils are frequent. The transport of the shell before being buried in the marine sediment and the hazards of fossilization and subsequent outcrop are reasons for do not discovering often full shells.
Cerithium giganteum (†) was first described by the famous naturalist Lamarck who, despite known for his misinterpretation of the mechanisms of evolution that Charles Darwin and Alfred Russel Wallace corrected, bequeathed an immense and precise work of classification of living beings.
The Cerithium genus of marine snails is still alive. Although, none of the current species exceeds 6 cm. Beautiful shells of Cerithium vulgatum and C.rupestre still can be collected in Catalan beaches.
The geological formation Santa Maria from sedimentary marine origin and from the Eocene epoch was initially described in the nearby county of Anoia. Geological formation Santa Maria sorts in following 3 members or subunits, from down to top: member Collbàs mostly made of sandy limestone, member Igualada mostly made of bluish mudstone, and, above, member Tossa dominated by limestone of coral origin. The member Tossa is dated from the Lower Priabonian period, about 35-37 million years old. It outcrops in counties of Bages and Moianès in a diagonal strip from northeast to southwest that goes from Collsuspina to Marganell through south of Moià, Calders, Navarcles, south of Manresa and Castellgalí.
Cerithium giganteum (†) appears only in two layers of sandy limestone with variable grain size of the Tossa member; the upper layer of Cerithium is located on top, the lower layer is located approximately at half the depth of the member Tossa. In addition to Cerithium giganteum (†), another gastropod, Velates schmideli (†), a snail with a poorly twisted, about 7 cm length shell, is usually found in the lower layer of Cerithium. The two Cerithium layers allow the accurate stratigraphic correlation amongst columns from different localities, despite lateral rock composition changes, depth of layers differences and further changes by faults. The Cerithium layers separate each other much more the northeast area (Collsuspina, Moià, Calders) because the coral reef is deeper than in the southwest (Manresa, Castellgalí).
The best preserved Cerithium giganteum (†) fossils appear as sown in fields where erosion has fully emptied the Cerithium layer and released the fossils on a new, flat surface at lower height.
The images show the inner moulds of fossils of Cerithium giganteum (†) in a stretch of the lower Cerithium layer in the range of Montlleó (Castellgalí) where they are very common, likely after transport and deposition once the animals died.
[photos Francesc Sardans and Jordi Badia]
Further information:
- “El Cerithium giganteum Lam. com a guia geològica de Bages (Catalunya)” [= Cerithium giganteum Lam. as a geological guidance of Bages (Catalonia)], in Catalan. Francesc Porta, Acta nr.2 del Grup Autònom de Manresa de la Institució Catalana d’Història Natural, 1980.
- “Els fòssils del Bages i del Moianès” [= The fossils of Bages and Moianès], in Catalan. Josep Biosca Munts, Museum of Geology Valentí Masachs.