Taphonomic patterns mimic biologic structures: diagenetic Liesegang rings in Mesozoic coleoids and coprolites

Abstract

Because of physiology of coleoids, their fossils preserve soft-tissue-remains more often than other cephalopods. Sometimes, the phosphatized soft-tissues, particularly parts of the muscular mantle, display dark circular patterns. Here, we showcase that these patterns, here documented for fossil coleoids from the Jurassic of Germany and the Cretaceous of Lebanon, superficially resemble chromatophores (which enable living coleoids to alter their coloration). We examined and chemically analyzed the circular structures in these specimens, describe them, and discuss their genesis. Based on their structure and color, we visually differentiate between three types of circles. By comparison with similar structures, we suggest that these structures are not biogenic but Liesegang rings, which formed due to reaction-diffusion processes very soon after death.

Distraction sinking and fossilized coleoid predatory behaviour from the German Early Jurassic

“…the anterior 68 mm are covered by a dark substance that might be ink-stained soft tissues and phosphatized mantle musculature (cf. Klug et al 2021). Posteriorly, the acute conus part is exposed.…”

“…As far as exceptionally preserved coleoids are concerned, the Posidonienschiefer shares its importance with other Fossillagerstaetten such as, e.g., the Carboniferous of Bear Gulch (Landman and Davis 1988;Mapes et al 2010Mapes et al , 2019Klug et al 2019), the Middle Jurassic of Christian Malford and Rixon Gate (Doyle and Shakides 2004;Wilby et al 2004;Donovan 2006;Hart et al 2016Hart et al , 2020, the Middle Jurassic of La Voulte-sûr-Rhône (Fischer and Riou 1982a, b;Charbonnier 2009;Kruta et al 2016), the Late Jurassic of Eichstätt, Nusplingen, Painten and Solnhofen (Fuchs 2006a(Fuchs , 2015Klug et al 2005Klug et al , 2010Klug et al , 2015Klug et al ,2016Keupp et al 2010), and the Late Cretaceous of Hâkel and Hâdjoula (Fuchs 2006b;Fuchs and Larson 2011a, b;Fuchs et al 2009;Jattiot et al 2015;Klug et al 2021). As pointed out by Clements et al (2016), the preservation and non-preservation of soft-tissues is linked with the original physiology of the coleoids.…”

Preservation of nautilid soft parts inside and outside the conch interpreted as central nervous system, eyes, and renal concrements from the Lebanese Cenomanian

“…Remarkably, soft part remains are quite commonly preserved in both ectocochleates (ammonites, nautilids) and endocochleates (decabrachian and octobrachian coleoids) in the platy limestones of Hadjoula (Lebanon). These have been described especially for coleoids in great detail (Fuchs & Larson, 2011a, 2011bFuchs, 2006aFuchs, , 2006bJattiot et al, 2015;Klug et al, 2020Klug et al, , 2021aWippich & Lehmann, 2004). As far as nautilids are concerned, the most detailed account was probably provided by Keupp et al (2016).…”

“…Hence, the greatest likelihood to discover soft parts of ammonoids or nautilids is given in such Konservat-Lagerstätten (= conservation deposits; Seilacher, 1970), where soft parts became quickly phosphatised or pyritised and aragonite shells were dissolved. There are records of cephalopod soft parts and there is some potential for such preservation in, e.g., the Ordovician Soom Shale in South Africa (Gabbott, 1999), the Devonian Hunsrück Slate in Germany (De Baets et al, 2013;Stilkerich et al, 2017), the Devonian Hangenberg Black Shale in Morocco (Klug & Vallon, 2019;Klug et al, 2016a), the Carboniferous of Bear Gulch (Doguzhaeva et al, 2007;Landman et al, 2010;Mapes et al, 2019), the Carboniferous of the Itararé-Formation in Uruguay (Closs, 1967;Lehmann et al, 2015), the Triassic Thaynes Group in the USA (Doguzhaeva et al, 2018), the Jurassic of Christian Malford and Dorset (Hart et al, 2020;Wilby et al, 2004Wilby et al, , 2008, the Jurassic of Eichstätt, Nusplingen, Painten and Solnhofen (e.g., Dietl & Schweigert, 2011;Fuchs, 2006a;Klug et al, , 2016bKlug et al, , 2021aKlug et al, , 2021bSchweigert, 2009Schweigert, , 2021, the Cretaceous of Germany Klug et al, 2012), and, last but not least, the Cretaceous of Lebanon (Engeser & Reitner, 1986;Fuchs & Larson, 2011a, 2011bFuchs, 2006aFuchs, , 2006bJattiot et al, 2015;Klug et al, 2020Klug et al, , 2021aLukeneder & Harzhauser, 2004;Roger, 1946;Wippich & Lehmann, 2004;Woodward, 1883…”

“…These often stunningly beautiful fossils commonly retain phosphatised remains of the soft parts. Concerning cephalopods, soft parts have been described from octobrachians and decabrachians (Engeser & Reitner, 1986;Fuchs & Larson, 2011a, 2011bFuchs, 2006b;Jattiot et al, 2015;Klug et al, 2021a;Lukeneder & Harzhauser, 2004), ammonites (Hoffmann et al, 2021;Keupp et al, 2016;Wippich & Lehmann, 2004), as well as nautilids (Keupp et al, 2016). Notably, the ectocochleates often display the jaws in situ associated with soft tissue remains.…”