The geologic period 495-430 million years ago, the second period of the Paleozoic era. Inserted between the original Cambrian and Silurian periods to clarify the distinctions between each, and settle overlapping claims to the fossil records by Sedgwick and Murchison, respective founders of each period. The fossils each claimed ended up in the new period instead. Named for its type area in Wales, and the Ordovices, a Celtic group once native to the region (much later than the fossil record, of course -- but you knew that).
Nothing much was doing on land, evolution-wise -- the continents lay bare. At sea, a major and rapid diversification of life forms occurred. With the departure of the trilobites and other forms at the end of the Cambrian, opportunities arose for many life forms, including brachiopods, worms, and sea lilies. Carnivorous molluscs were the dominant life form of the period.
A great Ice Age dominated much of this period, possibly caused by Gondwana travelling over the South Pole.
Back: The Cambrian period
On: The Silurian period