Survival of the thinnest: rediscovery of Bauer’s (1898) ichthyosaur tooth sections from Upper Jurassic lithographic limestone quarries, south Germany

摘要

The re-discovery of nine petrographic slides from the late 19th century at the palaeontological collections of the University of Zurich, showing thin-sectioned ichthyosaur teeth, revealed these slides be the only preserved remains of the historical collection of Upper Jurassic ichthyosaurs from the Bavarian State Collection for Palaeontology and Geology; fossil material which, up to now, was thought to have been completely destroyed during World War II. Here the history of these slides, from their origin in Munich as part of the doctoral thesis of Franz Bauer (1898) to their rediscovery in Zurich in 2010 is presented. Furthermore, a complete overview of all slides is given to elucidate their scientific value with the background of up-to-date knowledge of ichthyosaur dentition and tooth histology, including aspects of tissue and growth mark identification. As such, the sectioned teeth show an exposed layer of acellular cementum at the tooth neck, and sets of short and long period growth lines in the orthodentine. The slides of one tooth are part of the original syntype material of Aegirosaurus leptospondylus (Wagner). They reveal an oval rather than a rectangular shape of the root, as well as the presence of peculiar vascular canals, interpreted as secondary osteodentine deposition, in the peri-pulpal orthodentine.