Jellyfish, or scyphozoan medusae, play an important role in marine ecosystems as apex predators, and have probably done so since animals first appeared 550 million years ago. Unfortunately, preservation of such soft-bodied organisms in the fossil record is extremely rare. In central Wisconsin and New York, however, tens of thousands of medusae have been preserved in abundance in the Late Cambrian (about 500 million year-old) medium-grained orthoquartzites of the Elk Mound and Potsdam Groups. For my honors thesis, I am investigating these deposits in order to determine what circumstances permitted their preservation, to describe their anatomical features, and to classify them in an evolutionary context.

The circumstances that allow medusae to fossilize occur only rarely and are not well understood. These specimens occur in intertidal and sand flat facies, indicating extremely shallow to emergent conditions along the Laurentian shoreline. This suggests that the medusae may have been deposited as a result of stranding events. Additionally, these facies are associated with abundant microbial sedimentary structures, suggesting that microbial biofilms or mats may have facilitated preservation.



  
                                                      Possible Microbial Texture?

To better understand this highly unusual preservation I spent part of the summer of 2007 in Wisconsin collecting data on the local Cambrian deposits, studying their textural and taphonomic features, in order to deduce their depositional context. My next step has been to compare this material to the few other medusa deposits and specimens known from the fossil record. By studying the apparent anatomy of these speciments, and comparing them to that of known fossil and modern medusae, I hope to systematically classify them with greater certainty. Visiting a contemporaneous medusa deposit in New York allowed me to further determine what preservational conditions characterized Late Cambrian coastal systems, how widespread or confined these conditions were, and what range of fauna and flora they may have supported.

The deposits in Wisconsin and New York are an important resource for increasing our understanding of ancient medusae and the ecosystems that supported them, as well as of the evolutionary sequences which led to the development of their modern-day counterparts. By interpreting what environmental and geological conditions led to their preservation in the rock record, we will gain a better understanding of their mode of life.

Medusae from New York