Correlative tomography of exceptionally preserved Jurassic ammonite implies hyponome-propelled swimming

Lesley Cherns, Alan RT Spencer, Imran Rahman, Russell J. Garwood, Christopher Reedman, Genoveva Burca, Martin Turner, Neville Hollingworth, Jason Hilton

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Abstract

The extreme rarity of soft tissue preservation in ammonoids has meant there are open questions regarding fundamental aspects of their biology. We report an exceptionally preserved Middle Jurassic ammonite with unrivalled information on soft body organization interpreted through correlative neutron and X-ray tomography. 3D-imaging of muscles and organs of the body mass for the first time in this iconic fossil group provides key insights into functional morphology. We show that paired dorsal muscles withdrew the body into the shell, rather than acting with the funnel controlling propulsion as in Nautilus. This suggests a mobile, retractable body as a defence strategy and necessitates a distinct swimming mechanism of hyponome propulsion, a trait that we infer evolved early in the ammonoid–coleoid lineage.
Original languageEnglish
JournalGeology
Early online date7 Dec 2021
DOIs
Publication statusE-pub ahead of print - 7 Dec 2021

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