Intergrowth of Orbignyella germana Bassler, 1911 (Bryozoa) and Lambelasma carinatum Weyer, 1993 (Rugosa) in the pelmatozoanbryozoan-receptaculitid reefs from the late Ordovician of Estonia

Abstract

The earliest known rugosan-bryozoan intergrowth is reported from the early Katian of Estonia. A specimen of Orbignyella germana Bassler, 1911, from pelmatozoan- bryozoan-receptaculitid reefs of the Vasalemma Formation shows intergrowth with rugosans Lambelasma carinatum Weyer, 1993. The morphology of the bryozoan colony does not show any malformations or changes in zooid size near the embedded rugosans. It is likely that intergrowth between L. carinatum and O. germana was purely accidental. Relatively high population densities and restricted space for growth in the reef may have caused this intergrowth. Rugosans may have benefitted from this association in achieving a stable substrate in shallow and hydrodynamically active waters of the reef environment, whereas bryozoans obviously used corals as a substrate. Lambelasma may have been especially prone for intergrowth with bryozoans as it participates in three associations in the Late Ordovician of Estonia.