The dusky shark has a long streamlined body that is brown or gray above and white below. There is a faint lateral stripe that extends to the pelvic fin. Juveniles have a dark colouration on the tip of the caudal fin and the underside of the pectoral fins that is less pronounced in adults. The first dorsal fin is much larger than the second with a dermal ridge found between the two dorsal fins. The upper lobe of the caudal fin is larger than the lower lobe. The pectoral fins are long and curved on the trailing edge. The dusky shark can grow to 4 meters (13 feet) in length. The upper teeth of the dusky shark are broad and triangular with a serrated edge, but while the front teeth are virtually erect, the others are slightly oblique. The lower teeth differ since they have narrow, erect cusps with more finely serrated edges than the upper teeth.
- Dermal ridge between the first and second dorsal fin
- Upper and lower teeth nearly erect
- Nictitating membrane over eye
The diet of this shark includes small schooling fish such as sardines and anchovies, as well as larger fish like tuna, mackerel, flatfish and eels. The dusky shark also eats dogfish, catsharks, skates and rays.
Females become sexually mature at about 3.0 meters (10 feet), while males become sexually mature at 2.9 meters (9.5 feet). They are viviparous and females give birth to a litter of 6 to 14 pups. After 16 months gestation the pups are delivered at a size of approximately 95 cm (3 feet).
The dusky shark lives in warm temperate continental waters. The specimens captured in Canadian waters were found at a water temperature of 19 degrees Celsius.
This shark is found in the Atlantic, Pacific and Indian Oceans. In the western North Atlantic the northern most part of the range is Georges Bank. They continue to be found southward to the Caribbean Sea, the Gulf of Mexico and through to Brazil.