Cobelodus is an extinct genus of shark

Shark

Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....

 that lived in the Middle to Late Carboniferous

Carboniferous

The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...

 period in what is today Illinois

Illinois

Illinois is the fifth-most populous state of the United States of America, and is often noted for being a microcosm of the entire country. With Chicago in the northeast, small industrial cities and great agricultural productivity in central and northern Illinois, and natural resources like coal,...

 and Iowa

Iowa

Iowa is a state located in the Midwestern United States, an area often referred to as the "American Heartland". It derives its name from the Ioway people, one of the many American Indian tribes that occupied the state at the time of European exploration. Iowa was a part of the French colony of New...

.

Cobelodus was a 2 metres (6.6 ft) long predator. Although it was a shark, Cobelodus had a number of differences from modern forms. It had a bulbous head, large eyes, a high-arched back, and a dorsal fin placed far to the rear, above the pelvic fins. Because of its large eyes, it is thought to have lived in the deeper, darker parts of the sea, hunting crustacean

Crustacean

Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...

s and squid

Squid

Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...

. Another unusual physical feature of Cobelodus are the 30 centimetres (11.8 in) long, flexible cartilagenous

Cartilage

Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...

 'tentacles' sprouting from its pectoral fins. Their purpose is unknown.