There is an excellent and entertaining book on the development of zippers:
Robert Friedel's Zipper An Exploration in Novelty (1994) W.W.Norton & Co., NY.
Another interesting source of information on zippers can be found online, in this Zipper blog.
I have only found one very old zipper. It is marked "Pat Pend PALM" and I
found it in a c1900-1930 sewing basket. I could not find it in Friedel's
book, however it is most similar to the 1908 Plako fastener on page 52.