Role of the microorganisms in the post-mortem transformations in the shells of the phosphate brachiopods

The phylum Brachiopoda includes a small class Lingulata that first appeared in the Early Cambrian. These brachiopods were very numerous in the Lower Paleozoic, and still survive in the recent sea biota (five genera). Lmgulate shells consist of alternated organic and calcium phoshate layers, but lack calcium carbonate typical of another brachiopod class - Calciata. Calcium phosphate layers are composed of thin needle-like ciystallites enclosed in organic matrix. Thus the organics form more than half of the shell and, together with the soft body, it may be about three quarters of the entire organism. After the death the ungulate shells have undergone the intensive attack of microorganisms. According to Ch. Emig(1) data, the organic matter in recent Lingula shells near the bottom surface macerates and dissolves in a week, after that shells disappear. So the preservation of shells in fossils occur under certain conditions. Text below describes three different cases of shell preservation in fossils: due to intensive bacterial activities or, on the contrary, due to supressed bacterial work.