Shallow sea bustling with life

485 million years – 485 metres

Orthocones, trilobites and a sea star. (Walter Myers)

The surface of the oceans is at its highest. Animal diversification continues. The first vertebrates evolve. Corals, Orthocerai, moss animals, brachiopods, trilobites and the first vertebrates form limestone sediments in the Baltic Sea region.

Kuva: Animal life diversification continued. Here orthoceratites, trilobites and seastars are shown. Walter Myers

Early Ordovician period

Animal diversification continued. The increase in volcanic activity at the mid-oceanic ridges caused the oceanic basins to contract in volume, and the surface of the oceans to rise. Shallow seas were wide, and corals, moss animals, Brachiopoda and Trilobites formed layers of limestone in the Baltic Sea. During Ordovician, the Baltic sea had also nine meter long Orthocerai, relatives of modern squids. The first jaw-less vertebrates evolved. In continental Finland, only a few microscopic fossils have remained intact in the shelter of meteor craters.