Belemnite phylogeny

Belemnites are some of the most well-known fossils from the Mesozoic and are commonly used in geochemical studies due to their calcitic rostra that are relatively resistant to diagenetic overprint (Hoffmann & Stevens 2020). However, their evolutionary history is poorly understood, which has potential ramifications for the applicability of these methods due to undetected evolutionary constraints on rostrum geochemistry.

In this project, we attempt to reconstruct the phylogeny of belemnites using modern tools of Bayesian inference for the first time. A first study is already published, where we showed that previous classification concepts divided belemnites in groups that we have shown to be paraphyletic (Stevens et al. 2023). Instead, we suggested a revised phylogenetic classification of belemnites that shifts some of the formerly recognised families between Belemnitina and Belemnopseina, in addition to the recognition of a new unranked monophyletic group, the Pseudoalveolata (Fig. 1).

Fig. 1. Simplified belemnite phylogeny. From Stevens et al. (2023).

This study is only the first step, as the scarcity of characters means that there are still many uncertainties left. Ongoing work will test the applicability of further characters to belemnites (e.g., geochemistry), as well as investigating the phylogenetic position of belemnites within the cephalopod tree.

References

• Hoffmann, R. & Stevens, K. (2020). The palaeobiology of belemnites – foundation for the interpretation of rostrum geochemistry. Biological Reviews, 95(1), 94-123. https://doi.org/10.1111/brv.12557
• Stevens, K.*, Pohle, A.*, Hoffmann, R., & Immenhauser, A. (2023). Bayesian inference reveals a complex evolutionary history of belemnites. Palaeontologia Electronica, 26(1), a13. https://doi.org/10.26879/1239

*Contributed equally