How to build an ark – Understanding the evolutionary success of the Arcida (Bivalvia)

• Applicant: Professor Dr. Michael R.W. Amler
• Subject Area: Geology
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 503046147

The Arcida, the vernacular ark shells, are one of eight orders in the bivalve subclass Pteriomorphia, and a story of remarkable evolutionary success. The origins of the extant biodiversity of the Arcida and their genus-level phylogeny in the Palaeozoic and early Mesozoic are severely understudied and poorly understood. Three superfamilies are considered valid in the order Arcida, but only the Arcoidea, composed of seven families, persisted from the Ordovician to the Recent, and will be the focus of the project, because the relationships of Mesozoic survivors of the end-Permian mass extinction with their Palaeozoic ancestors are poorly established. The study will target the neglected Devonian to Early Triassic key interval of arcoid evolution. The key question regarding our understanding of the Arcida is both evolutionary and ecological: Why are ark shells so successful as a group? The family Parallelodontidae and related taxa represent the stem-group of the Arcoidea. Key questions and hypotheses to be tested are (A) Parallelodontidae, in their present configuration, are paraphyletic; Palaeozoic and Mesozoic representatives, although phylogenetically linked, represent different radiations. (B) Cenozoic ‘Parallelodontidae’ actually are Arcidae with convergent hinge features. (C) Palaeozoic Arcoidea are ecologically more diversified than their Mesozoic-Cenozoic counterparts. The project aims at an analysis of the palaeobiology, the origin and phylogeny, the taxonomy, the regional distribution and the palaeoecological evolution of this group. Apart from traditional morphological character analyses, all recently developed statistical methods will be applied. SEM analysis of shell microstructure, ontogenetic development from prodissoconch to dissoconch stages and the development of the hinge apparatus will be analysed for information on systematics and evolution. Morphometric and CT analyses will serve for a better understanding of the core group Arcoidea as a key for the whole order Arcida. Data sets generated during the project will be archived in MolluscaBase and Paleobiology Database.

• DFG Programme: Research Grants
• International Connection: United Kingdom
• Cooperation Partner: Dr. Simon Schneider
• Co-Investigator: Professor Dr. Patrick Grunert