Many people find fish and other underwater creatures strange, as well as interesting. We probably don't look all that interesting. We can't swim underwater for very long, and we must look very odd with two arms, two legs, and a head that all seem to be attached to a square torso. Yet fish, like humans, belong to the same major group of animals called vertebrates. Vertebrates also include reptiles, amphibians, and birds.
All vertebrates have an inner supporting skeleton, usually of bones, including a main backbone.
The bodies of all vertebrates are organized on a two-sided body plan. This means that our bodies can be divided down the middle and are more or less the same on both sides. Mammals have warm blood, and fur or hair, and breathe air. Most mammals have four limbs and are born rather than hatched. Infant mammals are fed on milk, supplied by a mother.