The phylogeny of belemnites: foundation for paleobiology and geochemistry

• Applicant: Professor Dr. Adrian Immenhauser, since 10/2022
• Subject Area: Palaeontology ; Systematics and Morphology (Zoology)
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 507867999

Belemnites (Belemnitida) were common coleoid cephalopods of Jurassic and Cretaceous seas. The low-Mg calcite rostrum, a part of their internal skeleton, is this group’s most common fossil remain. Belemnite rostra are exploited as geochemical archives, chiefly for paleotemperature reconstructions based on stable oxygen isotope (δ18O) and clumped isotope (Δ47) values, but evidence of carbon cycling dynamics based on carbon isotope (δ13C) data is of significance too. Moreover, belemnites are frequently used in paleoecological and paleogeographic studies, as well as biostratigraphy. Despite their significance, the above-family-level systematics of belemnites is still based on a nearly 60-year-old subdivision based on external features of the rostra and separates all belemnites into the two suborders Belemnitina and Belemnopseina. Belemnitina has long been considered to be paraphyletic, and for nearly all belemnite families it is unclear if they represent monophyletic groups. A preliminary cladistic study of belemnites, presented here, demonstrates that these suborders as traditionally defined are not monophyletic. In the proponent’s view, the lack of a belemnite phylogeny based on cladistic principles (i) hampers progress in paleobiological studies of belemnites and (ii) prevents a holistic view of the evolution and distribution of their micro- and ultrastructural features, as well as (iii) their geochemistry. Along these lines, the recently described triradial biphasic ultrastructure of belemnite calcite fibers has significant implications for interpreting belemnite proxy data. Based on the rostra’s newly described microstructural and geochemical characters, and in addition to established external features and ontogenetic data, the proponent intends to build a new, well-resolved cladistic phylogeny of belemnites. For this purpose, the rostra of 30 belemnite key taxa and closely-related aulacoceratids, featuring the ancestral rostrum, will be studied in detail employing state-of-the-art microscopical methods. These taxa are representative of the belemnites’ biodiversity, stratigraphy, and paleogeography. In addition to microstructural fabrics, high-resolution elemental data of well-preserved rostra will be tested as a new approach to belemnite phylogeny. The ontogenetic development of selected, (near-)pristine rostra of various taxa will be studied with high-resolution µCT-scanning to provide detailed and non-invasive information. The whole dataset will form a character matrix for the inference of belemnite phylogeny based on parsimony and Bayesian approaches. Results will be tested against the well-known stratigraphic ranges of the studied belemnite taxa. If successful, the here-proposed project will result in a well-resolved and time-calibrated phylogeny of belemnites that will be of considerable value for paleontologists, paleoecologists, and paleoceanographers.

• DFG Programme: Research Grants
• Co-Investigators: Dr. René Hoffmann; Dr. Robert Lemanis
• Ehemaliger Antragsteller: Dr. Kevin Stevens, until 9/2022