Sharks and rays are ancient, first appearing about 450 million years ago.

Sharks and rays may have the most advanced sensory systems—hearing, smelling, vision and electrical sensing—of all vertebrates.

As top predators, sharks and rays maintain the stability of many marine ecosystems.

In general, rays live on the bottom of the ocean and sharks in open water. A continuum of body shapes and lifestyles reflects the adaptation of these cartilaginous fish to a range of environments.

Scientists study the form and structure of fossils and living organisms in order to determine the diversity and evolutionary relationships of species.

Shark and ray reproduction varies, with some species laying eggs and some giving birth to live young.

Many shark and ray populations are endangered. All reproduce rather slowly, which makes them vulnerable to threats such as overfishing and the destruction of coastal breeding areas. Conservation efforts are underway, but populations are difficult to manage because much about these fishes remains unknown.