Developed in Turkey, India, and Iran in the 15th century, "zoomorphic calligraphy" is "not a matter of script metamorphosing into living forms which are also readable letters, but of using script to delineate such forms." That definition comes from a paper by Robert Hillenbrand, Professor of Islamic Art at the University of Edinburgh. This illustration, by Hassan Musa from Sudan, appeared in the 1994 book Mon Premier Dictionnaire Francais-Anglis Tout En Arabe. More info on the topic at BibliOdyssey. Link