A giant limulid trackway (Kouphichnium lithographicum) from the lithographic limestones of Cerin (Late Kimmeridgian, France) : ethological and environmental implications

International audienceA well-preserved large limulid trackway related to Kouphichnium lithographicum is described from the Upper Kimmeridgian Lithographic Limestones of Cerin (Ain, France). It is three meters long and exhibits ten successive sets of imprints characterized by a pair of well-preserved tetradactyl external imprints of legs VI (named pushers) and a variable number (mostly three pairs) of straight thin intermediate imprints (legs III-V). The trackway is unusually wide and was probably made by a very large adult approximately 38 cm wide and 80 cm long when related to the proportions of the modern Limulus polyphemus. The straightness of the trackway, the great repeat distance (stride), the length of series of leg imprints, their slight angle to the mid-line, the well-marked pusher (= leg VI) imprints and the absence of groove made by the telson all indicate fast progression of a vigorous animal on the sea-floor. This walking trackway can be easily differentiated from other limulid crawling, ploughing, and dying trackways usually found in lithographic limestones or other deposits of the geological record. Main characteristics of these different limulid trackways are evidenced. The occurrence of a living adult in the Cerin restricted lagoon is probably related to a brief period of connection with the open sea. This occurrence indicates either a passive introduction of the animal into the lagoon or a spawning behaviour