Taphonomy and Biodiversity of Fish Fossils from the Middle Devonian Milwaukee Formation
Andrew Rich ’20, Orland Park, Illinois
The fish fauna of the Devonian (Givetian) Milwaukee Formation in Milwaukee, Wisconsin, has been studied since 1876. However the preservation of these vertebrate fossils and paleoecological structure has not been examined in detail. This project investigates how fish fossils within the Milwaukee Formation were preserved and the biodiversity of this assemblage. This study determined that the preservation of this fossil fish assemblage was directly affected by the typically low energy levels punctuated by storm events and overall low levels of oxygen of the environment of deposition. This is seen by 100% of the fossil specimens represented by disarticulated remains, encrusters on fish plates, and an abundance of syndepositional pyritic replacement of fossils and carbonate matrices. This study found that the fish biodiversity was dominated by the class Placodermi, and Arthrodira and Ptyctidontida are the only distinct placoderms orders present. Furthermore the biodiversity of the Milwaukee Formation appears lower than world-wide trends of fish biodiversity among various other Givetian and Frasnian assemblages. This project contributes to the scientific knowledge surrounding the Milwaukee Formation by enhancing our understanding of the preservation of fish fossils, and by providing information on local and world-wide biodiversity trends in order to better document this important interval of fish evolution.