An iguana was a reptilian animal native to Earth. Iguanas could grow up to almost two meters long.
Charles Evans, in a fit of anger, turned Yeoman Tina Lawton into an iguana. (TOS: "Charlie X")
When Spot was affected by Barclay's Protomorphosis Syndrome, she turned into an iguana-like creature. (TNG: "Genesis")
Doctor Zimmerman created a hologram of an iguana that could speak in a slow, drawn-out low voice. He kept it as a pet, and named it Leonard. (VOY: "Life Line")