Sources and models
Ovid's relation to the Hellenistic poets was similar to the attitude of the Hellenistic poets themselves to their predecessors: he demonstrated that he had read their versions ... but that he could still treat the myths in his own way.
— Karl Galinsky
Ovid's decision to make myth the dominant subject of the Metamorphoses was influenced by the predisposition of Alexandrian poetry. However, whereas it served in that tradition as the cause for moral reflection or insight, he made it instead the "object of play and artful manipulation". The model for a collection of metamorphosis myths derived from a pre-existing genre of metamorphosis poetry in the Hellenistic tradition, of which the earliest known example is Boio(s)' Ornithogonia—a now-fragmentary poem collecting myths about the metamorphoses of humans into birds.
There are three examples of Metamorphoses by later Hellenistic writers, but little is known of their contents. The Heteroioumena by Nicander of Colophon is better known, and clearly an influence on the poem—21 of the stories from this work were treated in the Metamorphoses. However, in a way that was typical for writers of the period, Ovid diverged significantly from his models. The Metamorphoses was longer than any previous collection of metamorphosis myths (Nicander's work consisted of probably four or five books) and positioned itself within a historical framework.
Some of the Metamorphoses derives from earlier literary and poetic treatment of the same myths. This material was of varying quality and comprehensiveness—while some of it was "finely worked", in other cases Ovid may have been working from limited material. In the case of an oft-used myth such as that of Io in Book I, which was the subject of literary adaptation as early as the 5th century BC, and as recently as a generation prior to his own, Ovid reorganises and innovates existing material in order to foreground his favoured topics and to embody the key themes of the Metamorphoses.