Абстракт:

The evolution of shell colouration in Palaeozoic cephalopods is still poorly understood. To date, thirty-six species of orthoceratoids have been described that display colour patterns on their shell. Thirteen species are newly added herein or re-described from the Ludlow of Bohemia and two from the Mississippian of Belgium. The colour pattern is best documented in pseudorthoceratids. Some gaps in the fossil record still exist and seemingly separate periods dominated by specific types of shell colour patterns. Ordovician pseudorthoceratids have uniform, regular and evenly spaced longitudinal stripes. A similar but less regular type of colouration also occurs in Silurian pseudorthoceratids - rhythmised, irregular, interrupted and anastomosing colour stripes. After a gap in the Early Devonian, younger pseudorthoceratids possess a chevron pattern. A difference in the colour pattern in hatchlings and later growth stages is documented in the Carboniferous Pseudocyrtoceras. The restriction of colouration to the dorsal side of the shell in Devonian and Carboniferous pseudorthoceratids, which was previously interpreted as reflecting horizontal biological orientation of the shell and countershading, is questioned. The adaptive control and protective function of the shell colour patterns are indicated by the diversification of colour patterns in the Silurian, the emergence of the chevron pattern in the Devonian and early Carboniferous, the relationship between colour patterns and shell shape, the colour pattern polymorphism, and the ontogenetic changes in colouration. The pseudorthoceratid Pellucidoceras gen. nov. is established herein. Its type species, the Silurian P. decipiens, shows an intraspecific variability in the number, width, and spacing of stripes, and possibly represents case of colour pattern polymorphism.