Primozoan

The Primozoan period is the fourth and penultimate period of the Plutolithic era. Its name means "first (animal) life", as the oldest definitive animals are known from this period.

Life during the Primozoan was adapted to living in a relatively cold climate; however, the cold waters of the period were oxygen-rich, allowing the first filter-feeding large organisms to proliferate along the seafloor. Sponges, ctenophores, jellyfish, and a large host of unclassified frond-like organisms are known from this time. None of the organisms alive appear to be adapted towards eating other animals, but either filter-feeding in the water column or feeding from microbial mats on the seafloor. Stromatolites become much rarer at the end of the period, as bioturbation from grazing and burrowing animals disturbed the mud that stromatolites are made of.