Class Chondrichthyes
(chondro = cartilage, ichthyes = fish) are a diverse
and highly successful group of fishes that first appear in the
fossil record during the late Silurian.
As their name implies, they are characterized by a skeleton made entirely of cartilage, and are therefore commonly
referred to as the cartilaginous fishes. The group includes the
living sharks, skates, rays and chimaeras, as well as their extinct
relatives. They are the most primitive living jawed fishes. Chondrichthyans
occupy a number of different ecological niches within marine,
brackish and freshwater environments, and are remarkably resilient,
as is evidenced by their survival across mass extinctions for
over 400 million years.
