Final answer:
Mammals have a large brain-to-body ratio, which correlates with complex behaviors and increased intelligence. They have specialized features including hair, mammary glands, diverse diets, and adaptations for varied habitats. The brain-to-body ratio in mammals is a derived characteristic that signifies their advanced level of complexity.
Step-by-step explanation:
Mammals have many derived characteristics, including a large brain-to-body ratio. This ratio is significantly larger in mammals compared to other vertebrates and is linked with the complexity of behaviors due to increased cortical folding and surface area in the brain. Mammals possess unique characteristics such as hair, mammary glands, and specific features in their jaw, skeleton, integument, and internal anatomy. These distinctive traits are present in around 5,200 species that are categorized into monotremes, marsupials, and eutherian mammals.
Among mammals, primates have adaptations for climbing trees and larger brains relative to their body size. Different mammals show remarkable diversity in terms of their habitation, with some living in the ocean, like dolphins and whales, and others flying in the sky, such as bats.
The characteristics of mammals include living in social groups, having diverse modes of movement, and varying diets as herbivores, carnivores, or omnivores. Their hearts and lungs are adapted to supply their cells with ample oxygen and nutrients, supporting their active lifestyles. Mammals' intelligence is also relatively high due to their large brains.