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Taphonomic variation within a Middle Triassic fossil lagerstätte (Cassina beds, Meride Limestone) at Monte San Giorgio

  • Susan R. Beardmore
  • Heinz Furrer
Research Paper

Abstract

Middle Triassic sediments at Monte San Giorgio, a UNESCO heritage site on the Switzerland-Italy border, have famously sourced well-preserved vertebrate fossils. Taphonomic studies of reptiles in the Besano Formation and in the Cava inferiore, Cava superiore and Cassina beds of the Meride Limestone, and fish in the Besano Formation have already elucidated changes in palaeoenvironment through time in sediments that predominantly comprise black shale and carbonate lithologies. Saurichthys skeletons from the Ladinian Cassina beds were scored for articulation and completeness, with the resulting data sorted to test for variation among layers and lithologies in the 2.7-m thick section. The greatest abundance of skeletons was found in finely laminated sediments, a reduced number in event bed sediments and an absence in volcanic ash deposits. No particular bed showed better or worse preservation. The final state of a skeleton entering the fossil record was the result of the mode of deposition and rate of sedimentation with the additional influence of features at the sediment surface, notably microbial mat growth and its ability to stick carcasses to substrate.

Keywords

Saurichthys Middle Triassic Meride Limestone Taphonomy Microbial mat 

Notes

Acknowledgements

We thank C. Klug for access to specimens in the Paläontologisches Institut und Museum der Universität Zürich, Switzerland, and T. Brühwiler, C. Egli, J. Huber, H. Lanz, L. Pauli (all PIMUZ), C. Obrist (Rickenbach BL) and U. Oberli (St. Gallen) for their excellent preparation of specimens. The whole or partial preparation of more than 100 Saurichthys specimens from the Cassina beds was funded by the Swiss National Science Foundation (SNF) Sinergia grant CRSII3-136293 to M. Sánchez-Villagra, H. Furrer, and W. Salzburger. Lithologic sections during PIMUZ excavations were documented by H. Rieber (1971, 1972) and R. Schlatter and H. Schwarz (1973). The stratigraphic section and location map in Fig. 1 were produced by B. Jost and P. Furrer, and several images in other figures were taken by R. Roth. E. Maxwell (PIMUZ) assisted with the taxonomic identification of some specimens. M. Kuhn (Uster) provided generous support that enabled SB to study the specimens in Zurich. We also thank Øyvind Hammer for help with statistics and constructive comments on the manuscript in addition to those provided by Raymond Rogers and the editors.

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Copyright information

© Paläontologische Gesellschaft 2018

Authors and Affiliations

  1. 1.Oxford University Museum of Natural HistoryOxfordUK
  2. 2.Paläontologisches Institut und Museum der Universität ZürichZurichSwitzerland

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