Место издания: Florence , Год издания: 2004

The Ordovician can be regarded as one of the greatest critical periods in biosphere history in the context of ecosystem evolution. It was the time of crucial biotic events which radically altered structural, functional and spacial parameters of global biogeochemical system of the Earth. New ecologically specialized groups were the first to appear and reached their acme, providing a more efficient use, transfer, and transformation of matter and energy in ecosystems: articulate brachiopods and sessile colonial (tabulates, tetracorals, heliolitoids, and stromatoporoids), aggregated (crinoids), and colonial-aggregated (bryozoans) filter-feeding organisms with skeleton as well as ostracodes, first small aquatic universal eaters. The pelagic zone became a constant rather than facultative, as before, habitat for zooplanktonic and nektonic organisms: graptolites, radiolarians, conodonts, nautiloids, meroplankton (of colonial organisms), pelagic trilobites, ostracodes, and early primitive fish. Some spatial rearrangement of initial trophic level, major producers, took place in the same period: phytoplankton instead of benthic cyanobacteria became the main nutrient for heterotrophic organisms. This had a dramatic effect on the stage and lateral structure of trophic chains. These biotic events well correlate with global geological events: sharp increase in oxygen content in atmosphere and hydrosphere (appearance and acme of oxyphile heterotrophs), origin of ozone screen (occupation of epipelagic areas and margins in seas), volcanic enrichment of atmosphere with CO₂ (phytoplankton acme), the greatest Phanerozoic enlargement of epicontinental sea surface (and consequently the extension of marine photosphere, that was the main arena for benthic and pelagic life at that time). The comparative analysis of biological and geological data obtained for the Pre-Ordovician ecosystem reconstructions shows that the later are also associate with the change (in Earth outer shell) in the balance of two basic biosphere-producing gases: O2 and CO₂. Biological innovations in living systems at the initial stages of biosphere evolution were due to superstructure of new hierarchical levels: in the Proterozoic it was genetic level (appearance of genetic mechanism of reproduction in unicellular eucariots), in the Vendian (Neoproterozoic) cellular level (nonskeletal Metazoa), in the Cambrian organism level (skeletal hydrobionts), in the Ordovician coenosic level (trophic adaptation).