Species concept in palaeontology

PUBLICATION — Machalski, M., Owocki, K., Rasmussen, J.A. and Madsen, H. 2026. Ammonites of the Pachydiscus neubergicus group from the mid-Maastrichtian chalk of Denmark: alternative taxonomic interpretations. Acta Geologica Polonica, 76 (1), e70. doi.org/10.24425/agp.2026.158184

Map of Denmark with the location of the studied sites and an illustration of an ammonite with explanations of morphological terms

Figure: A. Danish localities which yielded studied ammonites of the Pachydiscus neubergicus group. B. Morphology and measurement of a P. neubergicus specimen.

Principles of species identification in fossil material are a fundamental problem in palaeontology. This paper illustrates the issue through a taxonomic analysis of a collection of ammonites of the Pachydiscus neubergicus group from the Maastrichtian chalk of Denmark. The specimens are internal moulds representing different ontogenetic stages, which, combined with the small sample size and the lack of precise stratigraphic control, prevents effective application of the population-based species concept. A conventional interpretation is presented: the material is divided into several species (morphospecies); however, it is likely that the analyzed individuals belonged to a single, morphologically highly variable biological species.

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