Early Silurian

Early Silurians were a Silurian subspecies identified by historians who had been allowed access to the "Monster Vaults" of the databanks in the Doctor's TARDIS. (PROSE: ) The corpse of one such Silurian was recognised by Vastra, a Late Silurian, as being of "scholar caste"; she in turn was identified on sight as a warrior by other Early Silurians. (COMIC: )

History
In 1835, Charles Darwin and the HMS Beagle expedition, along with the Sixth Doctor and Evelyn Smythe, encountered a rogue Silurian group in the Galápagos Islands. The leader of this group was Tulok, who claimed to be responsible for creating humanity's prehistoric ancestors via a forbidden breeding program. (AUDIO: '')

In the late 20th century a group of Early Silurians were awakened from hibernation by the energy from the nearby nuclear power research centre at Wenley Moor. After disagreement between Okdel L'da and Morka over a course of action, Morka won out, killing Okdel, and the Silurians tried to reclaim the planet from humanity by releasing a deadly virus. This plan was prevented by Dr Liz Shaw of UNIT and the Third Doctor, when they had the cure mass-produced. After this plan was thwarted, they tried using their molecular disperser to destroy Earth's van Allen belt, so that the sun's radiation would burn the humans to death while allowing the cold-blooded Silurians to survive, but Liz and the Doctor stopped them again when they overloaded the disperser and the facility's reactor. Despite the Doctor's best efforts to broker a peaceful solution, the Silurian base was bombed by UNIT by order of Brigadier Lethbridge-Stewart. (TV: Doctor Who and the Silurians)

In 1983, Sarah Jane Smith and K9, while visiting Warren Martyn's archaeological expedition in Egypt, discovered an underground city of Silurians and Sea Devils. Sarah Jane opened diplomatic relations with them. On her return to England, she contacted the Brigadier, who wished to make amends for his earlier mistakes. (COMIC: )

In the 67th century, the image of an Early Silurian appeared among the Perils of the Constant Division listed in a vid-briefing aboard the hospital ship Tsuranga. (TV: )

Alternate timelines
In an alternate timeline created by the Black Guardian where the First Doctor never left Gallifrey, and became Lord President, the Silurians and the Sea Devils fought over Earth with a number of alien invaders. This timeline was destroyed when the Seventh Doctor retrieved the Key to Time. (COMIC: )

Behind the scenes

 * J. K. Woodward, who worked on the Star Trek crossover Assimilation², released a piece depicting an early Silurian assimilated by the Borg.
 * A figurine of an original Silurian was released in the sixty-ninth issue of Doctor Who: Figurine Collection.