(2) The development of amphibians is metamorphosed through fertilized eggs, tadpoles, young frogs and adult frogs, and the morphological structure and living habits of young frogs and adult frogs are quite different.
(3) The reproductive development of D reptile is completely out of the limit of water, and it is the earliest and real terrestrial vertebrate. Reptiles have developed lungs and breathe with them.
(4)E is a bird with a streamlined body, wings on its forelimbs and feathers on its surface. Its physical structure and physiological characteristics are suitable for its flying life.
(5) Class F mammals have the reproductive development characteristics of viviparous lactation.
(6) Animals can be divided into vertebrates and invertebrates according to whether there are thorns in their bodies. Vertebrates have spines, while invertebrates have no spines. The main difference between A, B and C, D, E and F is that they have no spine on their backs.
So the answer is: (1) body part? (2) Abnormal development? (3) lungs? (4) forelimbs become wings? (5) viviparous breastfeeding? spine