This species is characterized by a snout that is slightly shorter than or as long as the width of the mouth, origin of the first dorsal fin over the free rear tip of moderately large falcate pectoral fins, and a low interdorsal ridge. Coloration Typical of many of the carcharhinids, the dusky shark is bluish gray above and white below. Tips of most fins dusky in younger sharks but inconspicuous in adults. Rep. NMFS Circ. 445 Upper teeth are triangular and slightly oblique with serrated edges.
Lower teeth are erect, narrowly cusped and more finely serrated.
Both sets of teeth become increasingly concave as they move distally in the jaw. The dermal denticles for C. obscurus are large, closely imbricated, and show five keels with five distinct pointed lobes. The denticles rest on a large rhomboidal base plate. Dusky sharks are very slow growing, mature at about 20 years and may live as long as 45 years. Feeding Behavior C. obscurus preys on a wide array of bony and cartilaginous fishes as well as a variety of invertebrates.