Crypsis in the pelagic realm: evidence from exceptionally preserved fossil fish larvae from the Eocene Stolleklint Clay of Denmark

• DOI: 10.1111/pala.12574
• Publication Date: 2021-09-14T07:45:51Z
• Authors: Miriam Heingård; Peter Sjövall; René L. Sylveste...; Bo P. Schultz; Johan Lindgren
• Keywords: Camouflage; Taphonomy

Abstract Marine deposits of earliest Eocene age in northern Jutland, Denmark, are renowned for yielding diverse teleost assemblages that have proved central enhancing our understanding the early evolution many extant actinopterygian clades. In this study, we investigate diminutive larval fish fossils from Stolleklint Clay, Ølst Formation, retain multiple soft‐tissue features preserved as distinct dark‐coloured stains. To examine elemental and molecular composition these soft parts, employed a combination time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS), scanning electron microscopy (SEM) energy‐dispersive x‐ray spectroscopy (EDS). Our analyses revealed structures contain chemically identifiable eumelanin intimately associated with densely aggregated microbodies morphologically consistent melanosome organelles. Thus, conclude carbonaceous represent traces originally melanized body including eyes peritoneum. Comparable pigmentation patterns seen larvae use semi‐transparency means camouflage pelagic environments, to suggest similar visual appearance Clay fossils. This turn suggests adaptations concealment UV‐protection had already evolved by beginning Eocene, notably during time interval characterized an extreme greenhouse climate, when global fauna become increasingly modern composition.