The Klerf Formation is an Early Devonian (Emsian) formation that includes a Lagerstätte in the Northern Eifel hills, at Willwerath near Prüm, Rhineland-Palatinate, Germany. In it Jaekelopterus rhenaniae, a giant eurypterid was discovered. The Klerf Formation, comprising greenish and reddish shales, siltstones and sandstones, was first described in 1919 by Rudolf Richter (1881-1957) and reaches a maximum thickness of about . It is part of Alken quarry along with Nellenköpfchen Formation.
Depositional environment
The siltstone and sandstone formation was deposited in an estuarine to deltaic environment. This was located on the edge of Avalonia bordering the Proto-Tethys Ocean.
Fossil content
Apart from the largest arthropod, Jaekelopterus rhenaniae, found in the formation, it also preserved other eurypterids (Adelophthalmus sievertsi, Parahughmilleria hefteri, Rhenopterus diensti, Pruemopterus salgadoi, Erieopterus sp.), possible xiphosuran (Willwerathia), terrestrial arachnids (Devonotarbus hombachensis, Xenarachne willwerathensis), some fish, bryozoa, brachiopod and ostracod remains, Mutationella indet. and flora.