Individuals of all species are separated from each other primarily by developmental age along PC1 (changes in FNP width, internasal distance, angle and width of nasal pits, width of oral cavity, distance between maxillary processes, size of eyes, and width of forebrain). Duck embryos are separated from chick and quail by changes in FNP and oral cavity width, forebrain height, head length, and eye size (along PC2, by species).