Template:Item/Series The Lost Ancients Series is a pair of book items. These items can be found with the 'unique' tag at Science HQ in World's End. However, it can also be found without the 'unique' label in The Great Library in Black Scratch.
The first book was written by the current leader of the Machinists, Finch and the second was written by Sabina.
The last paragraph of The Lost Ancients I cites that Sabina believes the Skeletons are the dominant inhabitants of X which is from Mass Extinction II. ru:Серия книг "Потерянные древние"