(A) ancV1R emerged in the common ancestor of bony vertebrates (black circle) and was lost in each of the common ancestors (gray circles) of teleost fish and of turtles, alligators, and birds (gray dashed lines and silhouettes). White silhouette and dashed black lines associated with shark indicate that ancV1R has not yet emerged.
(B) Examples of ancV1R loss events in higher primates (left) and cetaceans (right). The gray branches indicate the lineages in which ancV1R has been lost and the vomeronasal organ is absent. The timing of the mutations causing loss of ancV1R is shown above or below the gray circles.