Fibroblast Growth Factors (FGFs) are polypeptides with diverse activities in development and physiology. The mammalian Fgf family can be divided into the intracellular Fgf11/12/13/14 subfamily (iFGFs), the hormone‐like Fgf15/21/23 subfamily (hFGFs), and the canonical Fgf subfamilies, including Fgf1/2/5, Fgf3/4/6, Fgf7/10/22, Fgf8/17/18, and Fgf9/16/20. However, all Fgfs are evolutionarily related. We propose that an Fgf13‐like gene is the ancestor of the iFgf subfamily and the most likely evolutionary ancestor of the entire Fgf family. Potential ancestors of the canonical and hFgf subfamilies, Fgf4‐, Fgf5‐, Fgf8‐, Fgf9‐, Fgf10‐, and Fgf15‐like, appear to have derived from an Fgf13‐like ancestral gene. Canonical FGFs function in a paracrine manner, while hFGFs function in an endocrine manner. We conclude that the ancestral Fgfs for these subfamilies acquired this functional diversity before the evolution of vertebrates. During the evolution of early vertebrates, the Fgf subfamilies further expanded to contain three or four members in each subfamily. Developmental Dynamics 237:18–27, 2008. © 2007 Wiley‐Liss, Inc.