Abstract
The population dynamics of the fossil micromorphic brachiopods from shallow‐water Miocene deposits (calcareous clays to hard bottom of reef cavities) of the Roztocze Hills, south‐eastern Poland were studied by means of size‐frequency distributions. The following four species, which all also occur in the Recent Mediterranean, were used for the study: Megathiris detruncata (Gmelin), Argyrotheca cuneata (Risso), A. cordata (Risso) and Megerlia truncata (Linnaeus). The size‐frequency distributions for 28 assemblages studied here vary widely, even within a single species, from right‐skewed, through bell‐shaped to polymodal; no left‐skewed distribution was noted. The size‐frequency distributions with a large peak in the smaller size classes represent mostly assemblages collected from marly deposits. Those assemblages may be interpreted as inhabiting soft bottoms where small brachiopods are more vulnerable to burial by sediment and/or clogging effects on the lophophore apparatus. The assemblages collected from the reef cavities produced bell‐shaped size‐frequency distributions or distributions with a relatively high percent of larger individuals. This is because the protected hard bottom cryptic habitats are characterised by lower juvenile mortality and enable the brachiopods to reach a larger size. These results suggest that environmental factors play a crucial role in shaping brachiopod population structures, and that empty shells can be used to study population dynamics as well in Recent environments.