Actually, tortoise shell calls have been around a long time, at least back in the sixties that I can recall. Not sure how they got started or who thought of the idea. I suppose some creative turkey hunter must have found an empty shell, thought it would make a good sound chamber for a slate call, and the rest is history. I have had an empty shell for decades that I was planning on making a call with, but just never got around to it. Maybe somebody here has a more precise history for how they got started.