THE WAUKESHA BIOTA: AN UNUSUAL GLIMPSE OF LIFE ON A SILURIAN CARBONATE PLATFORM

The Waukesha Lagerstätte in the Brandon Bridge Formation (Silurian: Llandovery, Telychian) hosts a diverse, exceptionally preserved fauna. It is among the earliest deposits of exceptional preservation following the end-Ordovician extinction. Similar to a number of other Silurian Lagerstätten in Laurentia, it was deposited on a warm, shallow-marine carbonate platform. The Waukesha Biota includes an interesting assemblage of animals and plants, some of which are characteristic of Silurian epeiric seas, others of which are expected but rare in the Silurian, and still others that could be considered “holdovers” of groups more characteristic of Cambrian Lagerstätten.

Biomineralizing animals common in the Waukesha Biota include trilobites, conulariids, and Sphenothallus (holdfasts). Echinoderms, cephalopods, brachiopods, gastropods, bivalves, bryozoans, and corals, which are normally common in Silurian shelf lithofacies, are extremely rare or unknown. Non-biomineralizing or lightly skeletized arthropods, worms, and graptolites are common. Chordates and lobopods are present.

The Waukesha Lagerstätte could be considered as providing a skewed view of biodiversity in the Silurian. However, its existence was the result of specific taphonomic processes related to localized and unusual depositional conditions. Many of the taxa in this biota are represented by similar organisms in other less well-known Silurian Lagerstätten. Instead of a skewed view, the Waukesha Biota provides evidence of what was likely the true diversity found in Silurian shallow shelf environments of Laurentia.