Cobelodus is an extinct genus of shark that lived in the Middle to Late Carboniferous period in what is today Illinois and Iowa. 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 crustaceans and squid. Another unusual physical feature of Cobelodus are the 30 centimetres (12 in) long, flexible cartilagenous 'tentacles' sprouting from its pectoral fins. Their purpose is unknown.