Evolution and Systematics
The teeth of nurse sharks are always sharp and effective because new rows of teeth develop constantly to replace older, worn down teeth.
"Seen at close quarters, a nurse shark reveals a formidable array of backward-curving teeth. Sharks are relatively primitive fish, their skeletons, and hence their jaws, being made of cartilage rather than bone…This nurse shark has three rows of teeth in use at a time. As they grow, they slowly move forwards and eventually drop out -- they are probably in use for one or two weeks. But there are always rows of teeth developing behind to replace them. These teeth are larger than the ones currently in use, to keep pace with the shark's growth. It has been estimated that, over a period of ten years, some sharks produce, use and shed about 24,000 teeth." (Foy and Oxford Scientific Films 1982:87)
Learn more about this functional adaptation.
- Foy, Sally; Oxford Scientific Films. 1982. The Grand Design: Form and Colour in Animals. Lingfield, Surrey, U.K.: BLA Publishing Limited for J.M.Dent & Sons Ltd, Aldine House, London. 238 p.
Molecular Biology and Genetics
Statistics of barcoding coverage
|Specimen Records:||55||Public Records:||5|
|Specimens with Sequences:||34||Public Species:||1|
|Specimens with Barcodes:||16||Public BINs:||1|
|Species With Barcodes:||2|
|This article needs additional citations for verification. (January 2009)|
Ginglymostomatidae is a cosmopolitan family of carpet sharks, containing the three monotypic genera of nurse sharks. Common in shallow, tropical and subtropical waters, these sharks are sluggish and docile bottom-dwellers. Nurse sharks typically attack humans only if directly threatened.
The name nurse shark is thought to be a corruption of nusse, a name which once referred to the catsharks of the family Scyliorhinidae. The nurse shark family name, Ginglymostomatidae, derives from the Greek words ginglymos (γίγγλυμος) meaning "hinge" and stoma (στόμα) meaning "mouth".
The largest species, called simply the nurse shark Ginglymostoma cirratum, may reach a length of 4.3 metres (14 ft); the tawny nurse shark Nebrius ferrugineus is somewhat smaller at 3.2 metres (10 ft), and the short-tail nurse shark Pseudoginglymostoma brevicaudatum is by far the smallest at just 75 centimetres (2.46 ft) in length. The first of the three species may reach a weight of 110 kg. Yellowish to dark brown in colour, nurse sharks have muscular pectoral fins, two spineless dorsal fins (the second of which is smaller) in line with the pelvic and anal fins, and a tail exceeding one quarter the shark's body length.
The mouths of nurse sharks are most distinctive; it is far ahead of the eyes and before the snout (sub-terminal), an indication of the bottom-dwelling (benthic) nature of these sharks. Also present on the lower jaw are two fleshy barbels, chemosensory organs which help the nurse sharks find prey hidden in the sediments. Behind each eye is a very small circular opening called a spiracle, part of the shark's respiratory system. The serrated teeth are fan-shaped and independent; like other sharks, the teeth are continually replaced throughout the animal's life.
Nurse sharks are nocturnal animals, spending the day in large inactive groups of up to 40 individuals. Hidden under submerged ledges or in crevices within the reef, the nurse sharks seem to prefer specific haunts and will return to them every day. By night, the sharks are largely solitary; they spend most of their time rifling through the bottom sediments in search of food. Their diet consists primarily of crustaceans, molluscs, tunicates, and other fish, particularly stingrays.
Nurse sharks are thought to take advantage of dormant fish which would otherwise be too fast for the sharks to catch; although their small mouths limit the size of prey items, the sharks have large throat cavities which are used as a sort of bellows valve. In this way nurse sharks are able to suck in their prey. Nurse sharks are also known to graze algae and coral.
The mating season runs from late June to the end of July. Most nurse sharks are ovoviviparous, meaning the eggs develop and hatch within the body of the female, where the hatchlings develop further until live birth occurs. The gestation period is six months, with a typical litter of 30-40 pups. The mating cycle is biennial, as it takes 18 months for the female's ovaries to produce another batch of eggs. The young nurse sharks are born fully developed at about 30 cm long in Ginglymostoma cirratum. They possess a spotted coloration which fades with age.
Genera and species
- Genus Ginglymostoma J. P. Müller & Henle, 1837
- Genus Nebrius Rüppell, 1837
- Genus Pseudoginglymostoma Dingerkus, 1986 (proposed family Pseudoginglymostomatidae)