Our study examines the evolution of rapid metamorphosis and its endocrine control in desert-adaptes amphibians. New World spadefoot toads live in the deserts of the American southwest and breed in ephemeral pools where their one- two-week larval period is important to avoid desiccation. The closest relatives to the New World spadefoot toads, the Old World spadefoot toads (Pelobates) and parsley frogs (Pelodytes) of Europe, Asia, and North Africa, do not have accelerated metamorphosis and elucidate the endocrinological mechanism that allowed for its evolution in New World spadefoot toads