Vertebrate (noun, “VER-teh-bruht”)
A vertebrate is an animal with an internal skeleton and a spine, or backbone. This group includes reptiles, amphibians, fish, mammals and birds.
The vertebrate’s spine sets this group apart from invertebrates — animals that don’t have a spine. The vertebrate’s spine consists of linked-together bones called vertebrae. Usually, these vertebrae consist of bones. But some vertebrates — sharks and rays, for example — have vertebrae made of cartilage.
All vertebrates share some similar traits. In vertebrates, the spine runs the length of the body, starting at the head. The vertebrae surround and protect a crucial bundle of nerves called the spinal cord, which connects the brain and body. In all vertebrates, the spine is located on the dorsal side of the body — the side we might refer to as the back.
Beyond those shared traits, vertebrates vary wildly. In some, such as cats and kangaroos, the spine extends through a long tail. In others, including humans, the spine ends inside the body. Some vertebrates sport paired limbs, such as arms, legs, fins or wings. But other vertebrates — such as snakes — lack limbs altogether.
The smallest vertebrate is a raindrop-sized frog called Paedophryne amanuensis. This tiny hopper measures about 7.7 millimeters (0.3 inches). The largest vertebrate — the blue whale (Balaenoptera musculus) — measures up to 30 meters (98 feet).
Some vertebrates are endotherms, meaning they maintain their body temperature. Others are ectotherms. That means their body temperature changes with their surroundings. Some vertebrates are furred, some are feathered and some are scaled. Some vertebrates breathe through gills. Others use lungs. And some breathe right through their slippery skin.
In a sentence
Birds, bats and the now-extinct pterosaurs are the only three vertebrate groups known to have evolved the ability to fly.