- relating to or denoting the era between the Precambrian aeon and the Mesozoic era. Formerly called Primary.
The Palaeozoic lasted from about 570 to 245 million years ago, its end being marked by mass extinctions. The Lower Palaeozoic sub-era comprises the Cambrian, Ordovician, and Silurian periods, and the Upper Palaeozoic sub-era comprises the Devonian, Carboniferous, and Permian periods. The era began with the first invertebrates with hard external skeletons, notably trilobites, and ended with the rise to dominance of the reptiles