Cartilaginous Fishes - Chondrichthyes

Sharks, rays, skates, and chimaeras together make up a group of fishes known as the cartilaginous fishes (Chondrichthyes). This group includes the largest and most formidable marine predators alive today. Cartilaginous fishes are so named because instead of bony skeletons, their body frame consists of cartilage. Tough and flexible, cartilage provides enough structural support to enable these fishes to grow to incredible sizes. The largest of all cartilaginous fishes, and indeed of all fishes, is the whale shark.

Most cartilaginous fishes live in marine habitats all their lives, but a few species of sharks and rays live in freshwater during all or part of their lives. All cartilaginous fishes are carnivorous and most species feed on live prey. There are some species that feed on the remains of dead animals and still others that are filter feeders.

The Class Chondrichthyes is further divided into two subgroups, the Elasmobranchi (sharks, rays and skates) and the Holocephali (chimeras).

The earliest known cartilaginous fishes were ancient sharks that were descended from bony-skeleton placoderms. These primitive sharks are older than the dinosaurs. They swam in the world’s oceans 420 million years ago, 200 million years before the first dinosaurs appeared on land. Fossil evidence for sharks is plentiful but consists mostly of tiny remnants of the former fish—teeth, scales, fin spines, bits of calcified vertebra, fragments of cranium. Extensive skeletal remains of sharks are missing—cartilage does not fossilize like true bone.

By piecing together what shark remains do exist, scientists have uncovered a diverse and deep ancestry. Sharks of the past include ancient creatures such as Cladoselache and Ctenacanths. These early sharks were followed by Stethacanthus and Falcatus, creatures that lived during the Carboniferous Period, in a window of time referred to as the “Golden Age of Sharks”, when shark diversity blossomed to include 45 families.

During the Jurassic Period, there was Hybodus, Mcmurdodus, Paleospinax and eventually the Neoselachians. The Jurassic Period also saw the emergence of the first batoids: the skates and rays. Later came the filter feeding sharks and rays, the hammerhead sharks, and the lamnoid sharks (great white shark, megamouth shark, basking shark, sandtiger, and others).