Olcostephanus guebhardi as cryptic habitat for an Early Cretaceous coelobite community (Valanginian, Northern Calcareous Alps, Austria)

Upper Valanginian (Saynoceras verrucosum Zone) deposits of Upper Austria (Ternberg Nappe, Calcareous Alps) yield large numbers of specimens of Olcostephanus (O.) guebhardi (Kilian) showing unique epifaunal encrustations by placopsilinid foraminifera, bryozoans, and serpulids. The pattern of infestation clearly documents a 100% preference of the adherent taxa for the inner shell surface of the ammonites, whereas the outer surface remained barren. Such a remarkable cavity-dwelling palaeocommunity is described for the first time. Furthermore, the restriction of epifauna to almost a single ammonite species within an overall fauna of more than 13 ammonite taxa proves a strong taphonomic bias. This is interpreted as out-of-habitat mixing of Olcostephanus (O.) guebhardi.