Ontogeny of highly variable ceratitid ammonoids from the Anisian (Middle Triassic)

Eva Alexandra Bischof; Nils Schlüter; Dieter Korn; Jens Lehmann

doi:10.7717/peerj.10931

Ontogeny of highly variable ceratitid ammonoids from the Anisian (Middle Triassic)

PeerJ. 2021 Mar 2:9:e10931. doi: 10.7717/peerj.10931. eCollection 2021.

Authors

Eva Alexandra Bischof¹, Nils Schlüter², Dieter Korn², Jens Lehmann¹

Affiliations

¹ Geowissenschaftliche Sammlung, FB5 Geowissenschaften, Universität Bremen, Bremen, Germany.
² Museum für Naturkunde, Leibniz-Institut für Evolutions-und Biodiversitätsforschung, Berlin, Germany.

Abstract

Ammonoids reached their greatest diversity during the Triassic period. In the early Middle Triassic (Anisian) stage, ammonoid diversity was dominated by representatives of the family Ceratitidae. High taxonomic diversity can, however, be decoupled from their morphologic disparity. Due to its high phenotypic variability, the high diversity of ceratitids of the Anisian of Nevada was initially assumed to be caused by artificial over-splitting. This study aims to contribute data to settle this issue by applying geometric morphometrics methods, using landmarks and semi-landmarks, in the study of ontogenetic cross-sections of ammonoids for the first time. The results reveal that alterations in ontogenetic trajectories, linked to heterochronic processes, lead to the morphologic diversification of the species studied herein. Our knowledge, based on these ontogenetic changes, challenge the traditional treatment of species using solely adult characters for their distinction. This study furthermore demonstrates that the high diversity of the Anisian ammonoid assemblages of Nevada based on the traditional nomenclatoric approach is regarded to be reasonably accurate.

Keywords: Ammonoidea; Anisian; Beyrichitinae; Ceratitidae; Fossil Hill Member; Geometric morphometrics; Nevada; Ontogeny; Paraceratitinae; Phenotypic variation.

Grants and funding

This research received support from the German Science Foundation (DFG), project “Nevammonoidea” (LE 1241/3-1). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.