The Milwaukee Formation (Givetian, Wisconsin): gone but not forgotten

Abstract The Milwaukee Formation, a sequence of Givetian (Middle Devonian) marine strata deposited in what is now southeastern Wisconsin, USA, was recognized as preserving an exceptionally diverse biota of invertebrates, placoderms, and plants, when local cement companies mined the rock for the manufacture of hydraulic cement from 1876 to 1911. It is now recognized as containing one of North America's most diverse biotas of its age coming from a single formation, having roughly 250 species, 100 families, 16 phyla, and four kingdoms. Intense collecting has revealed the rich biodiversity that prevailed during the Devonian Period in what is now the Milwaukee area. When the cement mines shut down, the quarries were filled and what was already regarded as a localized series of outcrops became even more restricted. Today the formation is known almost exclusively from limited exposures in Estabrook Park and the adjoining Lincoln Park, in Milwaukee County, in the area once occupied by the cement quarries. These outcrops (the type locality) are protected by a Milwaukee County Park Ordinance that prohibits removing materials from the parks, thus enabling the type locality to remain intact for educational and non-destructive research purposes, while largely unstudied museum collections remain available for ongoing research.