Silurian era

The Silurian was an era of Earth history, prior to the great continental drift of 200,000,000 BC. After reading Dr Quinn's notes, the Third Doctor believed it was the era in which the Silurian race originated. (TV: Doctor Who and the Silurians) The Third Doctor later believed Dr Quinn got the period wrong, saying they should be from the Eocene era. (TV: The Sea Devils, PROSE: The Eight Doctors)

Behind the scenes
Doctor Who and the Silurians made the error of suggesting that the reptilian Silurians were from the Silurian era. The earliest reptiles evolved in the late Carboniferous, over 100 million years after the Silurian. The correction in The Sea Devils was insufficient, as the Eocene is millions of years before the earliest ape-like humans. The dating issue of the Silurians has persisted throughout Doctor Who media.