What structural feature distinguishes the famous Darwin's Finches from true finches (Fringillidae)?

Answer

They are actually members of the tanager family (Thraupidae)

Although commonly called finches, the Darwin's Finches of the Galapagos are genetically classified within the tanager family (Thraupidae), distinguishing them from the Fringillidae.

What structural feature distinguishes the famous Darwin's Finches from true finches (Fringillidae)?
birdanimaldescriptionfinch