Hungarian researchers have unlocked the secret of the extraordinary mandibular apparatus of Jurassic ammonites

Published in the prestigious Nature journal family’s Communications Earth & Environment, the discovery sheds new light on the lifestyle and nutrition of these ancient marine organisms, as well as the methodology for the structural analysis of fossils.

The basis of the research was the aptychus, a hard calcite-based “cover plate” that covered the lower jaw of the ammonites. It is the only organ that has been preserved with a high probability after the death of animals, and its mechanical resistance has long been a topic of discussion among professionals. 

“Calcite alone can’t explain the exceptional strength of the aptychus, so we assumed that there may be a special geometric structure responsible for it,” 

said Attila Demény, director of HUN-REN CSFK, who led the research.

The structure of the samples was examined by Electron Backscatter Diffraction (EBSD), and the spatial arrangement of the crystals was analysed using new mathematical tools developed at the Department of Morphology and Geometric Modelling of the Faculty of Architecture of the Budapest University of Technology and Economics (BME ÉPK) and the HUN-REN-BME Morphodynamics Research Group. Led by professors Gábor Domokos and András Sipos, the team developed a combinatorial and statistical model that can reconstruct 3D structures from 2D sections.

The results showed that the crystals are arranged in rotating, fibrous bundles, which, according to László Bujtor, one of the co-authors of the study, closely resemble a known geometric pattern, the so-called Bouligand-like structure. So far, this geometry has been observed in nature mainly in the chitin of crustaceans and insects, as well as in fish scales, where the twisting of the layers on top of each other ensures the outstanding resistance of the surface. This publication is the first to confirm this structure in a carbonate fossil, an organism hundreds of millions of years old.

“The appearance of the Bouligand-like structure indicates that the ammonites developed a mechanical solution already in the Jurassic period, which is used by modern organisms to achieve high resistance,” added Gábor Domokos, professor of BME. According to the authors, the strong crystal tissue may have played a large role in the ability of the ammonites to process hard-shelled prey, such as the remains of Saccocomids.

The research results go beyond paleontology: the combination of mathematical and microstructural analysis can be used in the study of other fossils and even geological features (such as crack networks). The method helps to recognize which parts of the fossils have retained their original chemical composition, which is important for paleoclimatological reconstructions or the determination of the palaeoclimate.

In addition to researchers from the BME, the HUN-REN CSFK, the Eszterházy Károly Catholic University and the University of Miskolc, the study also involved Eszter Ferencz, a fourth-year student of the Faculty of Architecture of the BME. The study was published in the journal Communications Earth & Environment under the title “Calcitic coverings of the lower jaw of Jurassic ammonites exhibit Bouligand-like structures”.

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