Biomineralizzazione e fosfato di calcio: considerazioni geologico-paleontologiche.

At the onset of hard-part mineralization, during the Precambrian-Cam¬brian transition, most of the organisms formed phosphatic skele¬tons. This event was probably related to a global phosphogenic episode re¬sulted from a prolonged period of anoxia during which high-phosphorus waters were formed in the deep ocean. At the end of the Proterozoic a phase of continental drift produced and in¬creased the rate of oceanic overturn and waters rich of phosphorus were upwelled to continental shelfs. High-phosphorus contents and the formation of extensive shal¬low epicontinental seas, which were available for colonization, caused the change from soft bodied to shelly faunas and the Cambrian radia¬tion event. The present status of knowledge regarding fossil records of the Precambrian-Cambrian transition is rewieved and a trend in the de¬position of hard parts is proposed.