Fantastic alphabet from the 15th century

I visited the Ashmolean Museum print room today and saw an engraved animated alphabet, by the Master E.S. These are very large letters, and each has a theme; sometimes real but exotic animals (a leopard–a chimpanzee — how did this German fellow see these?) or fantastic animals, or human beings of various occupations and types. It was made about 1460. Apparently no single museum has a complete alphabet, but you could see all the letters if you travel to Oxford, Berlin, and Dresden. The letters are large — too large for a book, which makes you wonder what they were meant for. Also, what was the fascination with letters, such that they provide the theme for a cycle of prints, like the seasons? Anything to do with printing presses?