Lepanto's cannon-armed galleys had earlier precedents

Did Lepanto see the first use of cannon on galleys?

No; it was a major demonstration of their importance, but cannon had already appeared on galleys.

Lepanto is corrected as a major example of artillery in galley warfare, rather than its first appearance. The presence of cannon on different vessel types explains why larger armed galleys and galleasses attracted attention. An opponent bringing cannon created pressure to answer with comparable firepower. The exchange concerns the significance of the weapons in battle, without giving a date for their first use on a galley.