It should be noted that Old Ones from Warhammer Fantasy World are not reptilian creatures. Their first creations - Slann and Lizardmen - of course are saurian-amphibian in nature, but Old Ones themselves were huge, tall humanoids, so it explains such antropomorphic dominance - Elves, Men, Dwarves, Ogres and so on are all creations of Old Ones also. Giants of Warhammer World are devolved Old Ones, and the last civilized strain of them were Sky Titans, peoples which lived in huge flying castles - later they were defeated by Ogre Kingdoms and even remnants are eliminated now. There are speculations exist, that Old Ones had connection to birth of an God Emperor in 40k (the most interesting lies in thought that GE may be the last Old One), but this is only speculations and fantasia.