In which of the following groups of vertebrates is parental care mostly exhibited ?

Parental care is mostly exhibited in Mammals (Mammalia). Mammals are unique among the vertebrates because they have mammary glands that produce milk to nourish their offspring. Parental care in mammals begins before birth with the development of the fetus inside the mother's uterus, where it receives nutrients and oxygen through the placenta. After birth, mammalian mothers provide their young with milk, warmth, and protection until they are able to fend for themselves. Mammalian fathers also play an important role in parental care. In many mammal species, fathers provide food, protection, and even grooming to their offspring. For example, male lions protect their cubs from predators while the mother is hunting, and male gorillas carry and play with their infants. While some species of reptiles, amphibians, and birds also exhibit parental care, it is not as extensive or complex as in mammals. In these groups, parental care may include behaviors such as guarding the eggs or young, providing food, or teaching the offspring how to find food and defend themselves. However, most reptiles, amphibians, and birds do not have specialized organs to produce milk or the ability to carry and nurse their young, which limits the extent of their parental care.