amphibians: A group of animals that includes frogs, salamanders and caecilians. Amphibians have backbones and can breathe through their skin. Unlike reptiles, birds and mammals, unborn or unhatched amphibians do not develop in a special protective sac called an amniotic sac.
birds: Warm-blooded animals with wings that first showed up during the time of the dinosaurs. Birds are jacketed in feathers and produce young from the eggs they deposit in some sort of nest. Most birds fly, but throughout history there have been the occasional species that don’t.
blue whale: A species of baleen whale (Balaenoptera musculus) that is the largest animal ever known to have existed. They can grow to lengths of 30 meters (almost 100 feet) and weigh up to 170 metric tons.
cartilage: (adj. cartilaginous) A type of strong connective tissue often found in joints, the nose and ear. In certain primitive fishes, such as sharks and rays, cartilage provides an internal structure — or skeleton — for their bodies.
dorsal: The back of something, usually an animal.
ectotherm: The term for an animal that relies on outside sources of heat to control its body temperature. This means their body temperatures will change as temperatures in their environment changes.
gills: The respiratory organ of most aquatic animals that filters oxygen out of water. Fish and other water-dwelling animals use gills to breathe.
limb: (in physiology) An arm or leg.
mammal: A warm-blooded animal distinguished by the possession of hair or fur, the secretion of milk by females for feeding their young, and (typically) the bearing of live young.
nerve: A long, delicate fiber that transmits signals across the body of an animal. An animal’s backbone contains many nerves, some of which control the movement of its legs or fins, and some of which convey sensations such as hot, cold or pain.
pterosaur: Any of various extinct flying reptiles of the order Pterosauria. These animals lived 245 million years ago to 65 million years ago. Although not true dinosaurs, they lived during the reign of dinosaurs. Among members of this order were the pterodactyls of the Jurassic and Cretaceous periods, which were characterized by wings consisting of a flap of skin supported by the very long fourth digit on each forelimb.
ray: (in biology) A term for members of kite-shaped fish in the shark family. They actually resemble flattened sharks with wide fins that resemble wings.
reptile: Cold-blooded vertebrate animals, whose skin is covered with scales or horny plates. Snakes, turtles, lizards and alligators are all reptiles.
shark: A type of predatory fish that has survived in one form or another for hundreds of millions of years. Cartilage, not bone, gives its body structure. Like skates and rays, sharks belong to a group known as elasmobranchs. They tend to grow and mature slowly and have few young. Some lay eggs, others give birth to live young.
spinal cord: A cylindrical bundle of nerve fibers and associated tissue. It is enclosed in the spine and connects nearly all parts of the body to the brain, with which it forms the central nervous system.
trait: A characteristic feature of something. (in genetics) A quality or characteristic that can be inherited.
vertebrae: (sing. vertebra) The bones that make up the neck, spine and tail of vertebrates. Bones in the neck are called cervical vertebrae. Bones in the tail, for animals that have them, are called caudal vertebrae.
vertebrate: The group of animals with a brain, two eyes, and a stiff nerve cord or backbone running down the back. This group includes amphibians, reptiles, birds, mammals and most fish.
whale: A common, but fairly imprecise, term for a class of large mammals that lives in the ocean. This group includes dolphins and porpoises.
