Konservat-Lagerstätten from the Upper Jurassic lithographic limestone of the Causse Méjean (Lozère, southern France): palaeontological and palaeoenvironmental synthesis

Since the 1980s, the Upper Jurassic lithographic limestone of the Causse Méjean (southern France) has been known by local naturalists to yield fossils. However, until the beginning of the 21st century, this plattenkalk remained largely undersampled and scientifically underestimated. Here, we present the results of two decades of prospection and sampling in the Drigas and the Nivoliers quarries. We provide the first palaeontological inventory of the fossil flora, the fauna and the ichnofauna for these localities. The fossil assemblages show the co-occurrence of marine and terrestrial organisms. Marine organisms include algae, bivalves, brachiopods, cephalopods (ammonites, belemnites and coleoids such as Trachyteuthis), echinoderms, decapod crustaceans (ghost shrimps, penaeoid shrimps and glypheoid lobsters) and fishes (including several actinopterygians and a coelacanth). Terrestrial organisms consist of plant remains (conifers, bennettitaleans, pteridosperms) and a single rhynchocephalian (Kallimodon cerinensis). Ichnofossils comprise traces of marine invertebrates (e.g. limulid trackways, ammonite touch mark) as well as coprolites and regurgitalites. Given the exquisite preservation of these fossils, the two quarries can be considered as Konservat-Lagerstätten. Both lithological features and fossil content suggest a calm, protected and shallow-marine environment such as a lagoon partially or occasionally open to the sea. Most fossils are allochthonous to parautochthonous and document diverse ecological habitats. Similarly to other famous Upper Jurassic plattenkalks of western Europe such as Solnhofen, Cerin or Canjuers, the Causse Méjean is a key landmark for our understanding of coastal/lagoonal palaeoecosystems during the Kimmeridgian–Tithonian interval.

A Long Mortichnial Trackway of Mesolimulus walchi from the Upper Jurassic Solnhofen Lithographic Limestone near Wintershof, Germany

A 9.7 metre long trackway was discovered in a plattenkalk quarry near the village of Wintershof, Bavaria; Germany in 2002. The huge ichnofossil derives from the Lower Tithonian, Upper Jurassic Solnhofen Lithographic Limestone. The trackway is complete from beginning to end and consists of footprints, telson drag impressions and is identified as the ichnotaxon Kouphichnium isp. Preserved at the very end of the trackway is a complete specimen of Mesolimulus walchi confirming the trackway as a mortichnia (‘death march’). Trackways and trace makers preserved together in the fossil record are rare and such specimens allow unique insights into behaviour and ecology. The events that led to M. walchi preserved in this sediment are unknown; however a most likely scenario is that the limulid was washed into the lagoonal environment during a harsh storm.