Palaeozoic
From Tardis Wiki, the free Doctor Who reference
The Palaeozoic was an era of Earth history which was part of the Phanerozoic eon. It included the Cambrian and Permian periods, and ranged from at least 500 million to 260 million 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.
