Meioscopic to microscopic capsules found in reddish, probably marine or brackish shales (Oligocene, Pannonian Basin; South Slovakia) are interpreted as possible trace fossils. They may represent burrows of meioscopic in-fauna.
Ferruginous walls of the capsules appeared very probably as late as during diagenesis; however, the (possibly organic) matrix had to exist before the diagenetic processes. Other discussed explanations (inorganic "ironstones"; coprolites) are not plausible.