Two – most difficult to access – Devonian Fossil-Lagerstätten with normally very rare echinozoans, here excellently preserved as natural archives, one with a possible attempt to escape obrution, the other wih indications of a very special way of life.

Both Lagerstätten were discovered many years ago and the two most unusual echinoderms in each were described: in Lagerstätte (‘archive’) I the armoured holothurian Prokrustia; in Lagerstätte (‘archive’) II the ophiocistioid Rotasaccus. Both Lagerstätten are burial (obrution) deposits. Due to the rarity of their very special echinoderms they represent important ‘natural archives’.

Natural archive I: In layers of the higher Talacasto Fm. (Lower Devonian) in the Precordillera (western Argentina) numerous obbrution Lagerstätten with diverse, very well preserved echinoderms were found, in one of them numerous specimens of the large Prokrustia which is completely skeletonised with large plates. Possibly, by new analytical methods the still unknown pharyngeal ring typical of holothurians will be detected. Special geopetal positions of Prokrustia will be will be discussed as unsuccessful attempts of escape lethal obrution.

Natural archive II: In finely laminated layers of the Wiedenest-Fm. (upper Middle Devonian of the Sauerland, eastern Rhenish Massif) there are several layers with some almost complete holothurians, but above all with thousands of jaw apparatuses (‘lanterns’ as in echinoids, but with typical, serially arranged angular teeth, "goniodonts") of Rotasaccus (a genus of the very rare echinoderm group Ophiocistioidea). As in some holothurians, its body wall of Rotasaccus is skeletonised with microscopic wheels, the wall of its very large podia with sieve plates. New ideas about the way of life of Rotasaccus are being discussed. Further important structures could possibly be visualised by using newer analytical methods on skeletons that partly are still calcitic.