JAMB - Biology (2000 - No. 7)
A characteristic of vertebrates that is unique to mammals is
the presence of pentadactyl limbs
parental care
the possession of scrotum
pulmonary circulation
Explication
unique characteristics of mammals include but not limited to ;
Most young are born alive, presence of a pair of testes inside a scrotal sac outside the body of the male, Brains better developed than in other classes of animal with superior intelligence, presence of hair or fur in the skin, presence of external ears as cartilagenous funnel like pinnae etc.