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Isolated ammonite soft body from the Late Jurassic of Eichstätt

2023-09-24 22:46 作者:从冥古宙走来  | 我要投稿

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


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 fnd 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 fnd 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.


Fig1 Soft parts of Subplanites sp. with a Strigogranulaptychus sp. from the early Tithonian of Wintershof near Eichstätt (Germany); SMNS 70,610. a Photo taken under white light. b Line drawing of the structures visible in the white light-photo (a) with possible interpretations

Fig 2 Soft parts of Subplanites sp. with a Strigogranulaptychus sp. from the early Tithonian of Wintershof near Eichstätt (Germany); SMNS 70610. a Photo taken under UV-light. b Line drawing of the structures visible in the UV-photo (a) with possible interpretations
Fig 3 Reconstruction of the internal anatomy of Subplanites as it came to rest on the sediment. Note that the interpretations of some organs such as the reproductive organ, the central nervous system, the hyponome and the gills are a matter of debate and represent only one possibleinterpretation out of several. The coiling of the soft parts corresponds to the coiled body chamber (ca. 300°), which was probably altered when these soft parts sank onto the sediment and came to a rest. a Reconstructed as in the fossil. b Organs arranged according to the conch 
Fig 4 Reconstruction of a possible sequence of events that led to the separation of the soft parts from the conch of Subplanites. a Acanthoteuthis attacks the ammonite and breaks the conch in the posterior half of the body chamber. b Acanthoteuthis withdraws the soft parts. Possibly, the arm crown remained attached to the aperture or was eaten away otherwise



Reference：

Klug, C., Schweigert, G., Tischlinger, H. et al. Failed prey or peculiar necrolysis? Isolated ammonite soft body from the Late Jurassic of Eichstätt (Germany) with complete digestive tract and male reproductive organs. Swiss J Palaeontol 140, 3 (2021). https://doi.org/10.1186/s13358-020-00215-7

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