Well-preserved Rothpletzella microencruster on a brachiopod shell from the Upper Ordovician of Estonia

A single shell of brachiopod Porambonites wesenbergensis Teichert, 1930 is encrusted in several places with thin sheets of Rothpletzella, tentatively assigned to R. gotlandica Wood, 1948, which are preserved as pyritized molds. The spheroidal shape of the pyrite is rare, as is its apparent nucleation on the calcitic walls of Rothplezella. Presumably, its calcareous sheaths were coated with organic films that provided substrate for heterogeneous nucleation. Comparable wall-directed nucleation was documented in the Ediacaran Conotubus, where pyritization initiates on the tube walls and progresses inward. The same brachiopod is also heavily encrusted by craniids and bryozoans. It is unclear whether the brachiopod P. wesenbergensis was encrusted postmortem or during its life.