Conasauga Fauna
Cambrian-age strata of western North America are world renowned for their fossils. The most famous is the Burgess Shale, an iconic example of a konservat-lagerstätte or deposit of exceptional preservation, found high in the Canadian Rockies of eastern British Columbia. Unusual depositional conditions inhibited scavenging and decay, permitting the preservation of biological soft tissue. These ghostly carbonaceous remains offer insight into aspects of 500 million year old organisms that are missing at other localities: trilobite legs and antennae, soft-shelled arthropods, lobopods, worms, sponges, algae, and a host of other “squishy” things. Similar preservation is also known from the Spence Shale, Wheeler Shale, and Marjum Formation of Utah, among other localities.
Fewer people know that rare cases of exceptional preservation are also found in the Cambrian of the eastern United States. The Conasauga Formation of Alabama and Georgia is Middle Cambrian in age, approximately equivalent to or slightly younger than the Burgess Shale. Certain beds within the Conasauga preserve faint remnants of soft tissue, including the soft-shelled trilobite relative Naraoia (better known from the Burgess Shale), red and green algae, and an assortment of sponges. Clusters of directionally aligned, conical hyolith shells have also been reported, possibly the gut contents of predatory priapulid worms.
These rare fossils co-occur with more typical Cambrian shelly fossils such as trilobites, inarticulate brachiopods, and hyoliths. The overall fauna is notably less diverse than the Burgess Shale, perhaps due its shallower depositional environment. However, even the Conasauga’s handful of exceptionally preserved fossils help to flesh out our knowledge of Cambrian ecosystems.