Collagen: graptolites’ strength

The work is a synthetic compilation of data on the walls of graptolite colonies, Ordovician and Silurian index fossils. The walls of graptolites are composed of collagen fibrils, forming unique half-rings (fuselli) and bands resembling bandages. Collagen fibrils of fuselli form a spongy structure, while bandages have densely packed, parallel fibrils. A unique group of graptolites are the Silurian retiolitines (Retiolitinae), in which bandages form a mesh of rods (lists). Thanks to the differentiation of collagen fibrils, their combinations and the creation of different structures, the walls of graptolites are strong and flexible.

Figure: A Monograptid Saetograptus leintwardinensis, B comparison of spongy fusellar fibrils with parallel cortical fibrils (SEM), C cortical bands (SEM), D retiolitid Retiolites geinitzianus (A. Kozłowska drawings, not scaled).