ANIMAL BEHAVIOR FROZEN IN TIME: THREE EARLY JURASSIC ERYONID LOBSTERS IN AN AMMONOID SHELL

A spectacular slab of Posidonia Shale (Lower Jurassic, lower Toarcian) from Dotternhausen in southern Germany was found to contain three delicate eryonid lobsters preserved within a flattened ammonoid shell of Harpoceras falciferum. Detailed determination of the lobsters was not possible as many key features were obscured due to compression. The three similarly sized specimens are preserved more than halfway within the body chamber toward the phragmocone and are closely spaced together, with the tails pointing toward each other. We interpret these specimens to represent corpses rather than molts and show that the specimens were not transported into the ammonoid shell. Instead, the lobsters sought shelter in preparation for molting or against predators such as predatory fish that were present in Dotternhausen. Alternatively, the soft tissue of the ammonoid may have been a source of food and attracted the lobsters, or it may have served as a long-term residency for the lobsters (inquilinism). This is thought to be the first example of gregariousness amongst lobsters in the fossil record. Moreover, it is one of the oldest known examples of decapods preserved within cephalopod shells.