Calcitic coverings of the lower jaw of Jurassic ammonites exhibit Bouligand-like structures
Attila Demény, László Bujtor, Gábor Domokos, András A. Sipos, Csaba Farkas, Eszter Ferencz, Boglárka Topa, Máté Leskó & Norbert Zajzon
Abstract: Well-preserved layered structures have been reported for Jurassic ammonites’ aptychi, but the role, function, and origin of the lamination has been unclear. Here, we applied electron backscatter diffraction imaging to detect crystal fabric patterns in the laminated layer of Laevaptychi (calcitic coverings of the lower jaw of Aspidoceratoidea ammonites) and their diagenetic alteration, which was used to interpret variations in stable oxygen isotope compositions. We combined electron backscatter diffraction imaging with discrete and combinatorial geometry to model the calcite crystal deposition patterns. A new probabilistic approach was developed to gain a fundamental 3D description of the tiling based on information from 2D sections. The analyses revealed that the lamination results from variable deposition of elongated calcite crystals arranged in rotating bundles, which may be interpreted as a Bouligand-like structure. Our finding is one of the earliest occurrences of Bouligand-like structure in non-chitinous, carbonate-based organs of molluscs.
