The Palaeozoic was an era of Earth history which was part of the Phanerozoic eon and included the Cambrian era. The Cambrian ended around 500,000,000 BC. (AUDIO: Power Play)
Biology
Horseshoe crabs were arthropods from the Palaeozoic. (PROSE: The Southwell Park Mermaid)
The Ediacara biota went extinct at the end of the Cambrian era. (AUDIO: Power Play)
References
Martha Jones once thought about how "tomorrow" she could be sightseeing in the Palaeozoic Era. (PROSE: Wishing Well)
Behind the scenes
The Palaeozoic Era contained the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian periods.