the Monster Manual, of course, notoriously plundered literature for it's critters, everything from Tolkien to mythology to fantasy literature. ERB seems to have had some influence, as noted earlier.... although EGG didn't seem to take much from Pellucidar. The lizard men might have been taken directly from the Horibs in one Pellucidar novel, but EGG ignored several other neat critters... the Mahars, the Trodon, etc.