Fig. 4: Evolution of Shh and Fgf8 expression among representative amniote taxa.

Expression of Fgf8 (blue) and Shh (red) in early stages of head development in lizard (Anolis sagrei), chicken (Gallus gallus)^2,36,37,38 and mouse (Mus musculus)^5,15,35,37. Images not to scale. N nasal pit, Mxp maxillary process, Mp Mandibular process.