The Prastaki were an alien species from the Thunderhead Spiral Galaxy.
Once Sarah Jane Smith unwillingly carried a plague of Squaleen locusts home with her after visiting a Prastaki trading ship. (PROSE: The Day of the Clown)
Behind the scenes
According to a DVD Extra of the second series of the Sarah Jane Adventures, the Tunguska Scroll was salvaged from a Prastaki trading vessel in 1908.