A shared derived trait involves shared characters that lineages have in common, which have evolved in the lineages leading up to a clade and that sets members of that clade apart from other individuals.
The four limbs is found in virtually all amphibians, turtles, lizards, snakes, crocodiles, birds, and mammals. It might not be seen in snakes now, but historically it is believed that ancient snakes once possessed limbs. This feature is a shared derived trait that exist among the selected clade.
