TAPHONOMIC VARIANCE IN EXCEPTIONAL PRESERVATION FROM THE MAZON CREEK LAGERSTATTEN

Fossils from the Pennsylvanian Mazon Creek (Francis Creek Shale) region of northeastern Illinois represent a rare instance of exceptional soft-tissue preservation in the fossil record. Organisms were rapidly buried and digenetically encapsulated within siderite concretions allowing for soft-tissue preservation. The fossils consist of a vast array of plants as well as diverse marine and terrestrial animals. An extensive concretion collection is reposited at the Royal Ontario Museum (ROM), allowing for comprehensive studies of the preservational variance occurring within, and between, species of differing integument types. Over 1,180 individuals across a broad spectrum of clades and tissue-types including juvenile vertebrates (Esconicthys), assorted fern leaves (Pecopteris), crustaceans (Belotelson, Acanthotelson, Anthracaris, and Anthrocauphosia), polychaetes (Esconites), a variety of hexapoda, and poorly-understood problematica (Tullimonstrum gregarium) were compared. Detailed matrices were constructed to evaluate the preservational variance on a character-by-character basis, in addition to evaluating the overall preservational quality across hundreds of individuals. Datasets were statistically compared through rigorous multivariate techniques including Principal Coordinate Analysis (PCO) and non-metric Multidimensional Scaling (nMDS) to find relative preservational trends. Ultimately, the construction of qualitative and quantitative taphonomic series of numerous anatomical structures between a large number of individuals may help constrain relative rates of decay, sequences of character loss, and allow inference of original tissue labilities and taphonomic trajectories in extinct organisms.