Coprolites from shallow marine deposits of the Nanjemoy Formation, Lower Eocene of Virginia, USA

The Eocene Nanjemoy Formation crops out on the Maryland and Virginia Coastal Plain, along the eastern coast of the United States. This formation is composed of sands, silts and clays and is divided into the Potapaco and Woodstock members. Remains of fishes, reptiles, birds, mammals, molluscs, fruits and seeds are common in the Potapaco Member, in addition to vertebrate coprolites. Here, we present an analysis of more than 2000 coprolites from the Fisher/Sullivan Site in Virginia. The chemical composition (phosphatic) and the type of inclusions (fish bones) indicate that only scats of carnivorous animals were preserved. The analysed specimens were grouped into six morphotypes: (1) the cylindrical morphotype is a cylinder with rounded ends; (2) the segmented morphotype is a cylinder segmented with rounded ends, and occasionally one end is concave; (3) the oval morphotype represents a bean-shaped coprolite; (4) the scroll morphotype is cylindrical to conical in lateral view and has coils seen only at the ends; (5) the folded morphotype is a spiral that is concentrically folded; and (6) the sinuous morphotype is serpentine, with rounded ends. Coprophagy-related scrape traces occur in different morphotypes and represent both invertebrate burrows and bite traces made by fishes. The mineralogical and chemical analyses indicate an early precipitation of phosphate and pyrite minerals, probably induced by the microbial community. All coprolites at the Fisher/Sullivan Site were produced by fishes: carcharhiniform sharks for the scroll morphotype and lamniform sharks, probably the genus Carcharias, for the folded morphotype; the oval, cylindrical and segmented morphotypes were likely produced by actinopterygian fishes.