Failed prey or peculiar necrolysis? Isolated ammonite soft body from the Late Jurassic of Eichst\xe4tt (Germany) with complete digestive tract and male reproductive organs

Christian Klug,Helmut Tischlinger,Günter Schweigert,Helmut Pochmann

doi:10.1186/s13358-020-00215-7

Abstract

Ammonoid soft parts have been rarely described. Here, we document the soft parts of a perisphinctid ammonite from the early Tithonian of Wintershof near Eichstätt (Germany). This exceptional preservation was enabled by the special depositional conditions in the marine basins of the Solnhofen Archipelago. Here, we document this find and attempt to homologize its parts with various organs such as the digestive tract, reproductive organs, the mantle cavity with gills, and the hyponome, with differing degrees of reservation. Alternative interpretations are also taken into account. We suggest that the soft parts were separated from the conch either taphonomically (following necrolytical processes affecting the attachment structures) or during a failed predation, where a predator (fish or coleoid) removed the soft parts from the conch but then dropped them. This find is interesting because it adds to the knowledge of ammonite anatomy, which is normally hidden in the conch. The reproductive organs show traces of what might have been spermatophores, thus supporting the hypothesis that the microconchs represented the males.

Highlights

Ammonoid soft-part preservation requires depositional conditions as found in conservation deposits, the specimen published by Hollingworth and Hilton (1999; see Klug and Lehmann 2015) shows that unusual preservation might occur in unexpected sedimentological contexts
Most ammonoid materials preserving remains of the soft parts come from conservation deposits worldwide
Description The main specimen SMNS 70610 is a limestone plate with remains of an ammonite (Figs. 1, 2). We assign these remains to the genus Subplanites based on the presence of a Strigogranulaptychus, the early Tithonian age of the sediments in the quarry at Wintershof, and the abundance of representatives of this genus at that locality

Summary

Introduction

Ammonoid conchs and jaws are known in great detail from a plethora of publications, while reports of identifiable soft parts are exceedingly rare or doubtful (Kolb 1961, 1967; Closs 1967a, b; Zeiss 1968, 1969; Stürmer 1969; Otto 1994; Hollingworth and Hilton 1999; Schweigert and Dietl 1999; Klug and Lehmann 2015; Lehmann et al 2015; Klug et al 2019; Donovan and Fuchs 2016; Clements et al 2016; Mapes et al 2019). These include specimens from the Late Devonian of Morocco (Klug et al 2016a, b), the Early Carboniferous of Bear Gulch (Landman et al 2010; Klug et al 2019; Mapes et al 2019), the Late Carboniferous of Paraguay (Closs 1967a, b; Bandel 1988; Lehmann et al 2015), the Permian of the USA (Tanabe et al 2000); the Early Triassic of Greenland (Lehmann 1985), the Middle Triassic of Germany (Klug and Jerjen 2012), the Late Triassic of Austria (Doguzhaeva et al 2004), the Early Jurassic of Germany (Lehmann and Weitschat 1973; Wetzel 1979; Lehmann 1985; Riegraf et al 1984) and Great Britain (Lehmann and Weitschat 1973), the Middle Jurassic of Russia (Mironenko 2015a), the Late Jurassic of Germany (Schweigert and Dietl 1999; Mapes et al 2019), as well as the Late Cretaceous of Lebanon (Wippich and Lehmann 2004) and of Germany (Klug et al 2012, 2015).

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Conclusion