The skeletal taphonomy of anurans from the Eocene Geiseltal Konservat-Lagerstätte, Germany: insights into the controls on fossil anuran preservation

The Geiseltal biota is a lacustrine-hosted Konservat-Lagerstätte from the Eocene of central Germany. Despite its rich fauna and flora that is represented by at least 50,000 fossil vertebrates, insects and other invertebrates, plants and trace fossils, the taphonomy of the biota is still poorly understood. In particular, the anurans have not been the focus of taphonomic investigation. Here, we analysed the skeletal taphonomy of 168 anurans from Geiseltal and scored each specimen for orientation, completeness and articulation. Most specimens are partial skeletons that were truncated during preparation. This process introduces measurable artefacts into the taphonomic data and should be assessed in future taphonomic studies on fossil vertebrates. The Geiseltal anurans show several recurring taphonomic states, including disarticulation or loss of abdominal bones, loss of one or more limbs, extensive disarticulation and extensive loss of elements across the body. Relatively rare taphonomic states include loss of distal limb elements only, scattered bones and isolated, articulated limbs. These data are the basis of a new taphonomic model for the Geiseltal anurans. Comparative analysis of patterns in completeness and articulation in these specimens and in fossil anurans from other Cenozoic Lagerstätten reveals repeated taphonomic patterns in anuran preservation in lacustrine-hosted settings, such as proximal to distal trends in completeness, preferential loss of small peripheral bones, disarticulation of abdominal bones and reorientation of major body regions and limbs. The taphonomic controls in lacustrine systems are surface water temperature, lake depth, vegetation, exposure to bottom currents, transport mechanisms, extent of scavenging, decay regime, bone size and bone location in the skeleton. In turn, these are ultimately controlled by palaeoclimate, lake physiography and hydrology, and anuran anatomy. A universal approach to quantitative analysis of skeletal taphonomy metrics will allow comparative testing of the relationship between preservation and palaeoenvironment for diverse fossil vertebrates.

Methods
Date of data collection: 02/2019–11/2020

Geographic location of data collection: Natural Sciences Collections (ZNS), Halle (Saale), Germany.