The correct answer is option 4: Birds. Pneumatic refers to the presence of air-filled cavities within bones. These air-filled cavities, also known as pneumatic bones, are found in birds. These hollow spaces help to reduce the weight of the bird`s skeleton, making it easier for them to fly. The air sacs connected to the lungs of birds extend into the bones, filling them with air and making them lightweight yet strong enough to withstand the stresses of flight. This adaptation is unique to birds and is not present in fishes, amphibians, or reptiles.