External nares and olfactory perception.
Lower vertebrates have more widely separated external nares than higher forms and are thus better adapted to utilize olfactory tropotaxis, or stereolfaction, than higher vertebrates which, on account of their flexible necks, must utilize klinotaxis. Snakes and tubenosed bats break the rule on account of their specialized life styles.
D000818:Animals; D009666:Nose; D012886:Skull; D012903:Smell; D013045:Species Specificity; D014714:Vertebrates