Author: Gill, 1862
Field Marks:
Small to large sharks with nasoral grooves but no perinasal grooves and folds, short to long barbels, small transverse mouths in front of eyes, small spiracles behind but not below eyes, no lateral skin flaps on head, two spineless dorsal fins and an anal fin, the second dorsal origin well ahead of the anal origin, and a short precaudal tail much shorter than the head and body.
Diagnostic Features:
Body cylindrical or moderately depressed, without ridges on sides. Head broad and flattened, without lateral flaps of skin, snout truncated or broadly rounded; eyes dorsolaterally or laterally situated on head, without subocular pockets; spiracles much smaller than eyes, behind but not below them; gill slits small, fifth virtually overlapping fourth; internal gill slits without filter screens; nostrils with short to moderately long, pointed barbels but without circumnarial folds and grooves; mouth moderately large, subterminal on head, and transverse, without a symphyseal groove on chin; teeth not strongly differentiated in jaws, with a medial cusp, lateral cusplets and weak labial root lobes; tooth rows 24 to 38/22 to 32. Caudal peduncle without lateral keels or precaudal pits. Dorsal fins equal-sized or first dorsal larger than second, first dorsal with origin varying from slightly anterior to the pelvic origins to over their bases, and insertion just behind the pelvic insertions; pectoral fins moderately large, broad and rounded to narrow and falcate, larger than pelvic fins, with fin radials partially expanded into fin web but falling short of its distal edge; pelvic fins somewhat larger to somewhat smaller than dorsals and anal fins; anal fin about as large as second dorsal, with its origin about opposite second dorsal origin or midbase; anal fin with broad base and angular apex, separated by a space much less than base length from lower caudal origin; caudal fin with its upper lobe at a low angle above the body axis, less than a third as long as the entire shark, with a strong terminal lobe and subterminal notch but no ventral lobe or a very short one. Supraorbital crests present on cranium, these laterally expanded. Valvular intestine of ring type. Colour plain or with dark spots in young.
Habitat, Diatribution and Biology:
These are common, small to large, nocturnal, inshore bottom sharks with a circumglobal distribution in subtropical and tropical continental and insular waters, in depths from the intertidal down to at least 70 m. They occur on coral and rocky reefs, in sandy areas, in reef lagoons, mangrove keys, and at the surf zone, usually close inshore and sometimes in water deep enough only to cover them. At least two of these species occur in groups while resting on the bottom, often Iying atop one another. One species (Ginglymostoma brevicaudatum) is a small shark attaining a length of less than 1 m, but the others are large, bulky sharks reaching over 3 m.
Development is ovoviviparous in at least one species (Ginglymostoma cirratum), with young that are nourished primarily by yolk while in the uterus; litters of 20 to 30 young have been reported. Another species (Nebrius ferrugineus) is variously reported as ovoviviparous or oviparous.
These sharks cruise and clamber on the bottom with their mouths and barbels close to the substrate while searching for food; when they contact a food item, they reverse and use their short, small mouths and large mouth cavities as a bellows to suck in their prey. The presence of small, active reef fishes in the stomachs of large, seemingly clumsy nurse sharks suggest that they may stalk and suddenly suck in such items, or alternatively merely inhale them in when the prey fishes are torpid and Iying on the bottom at night. Food items include a variety of bottom and reef organisms, bony fishes, crabs, shrimps, lobsters, and other crustaceans, squids, octopuses, and other molluscs, corals, sea urchins and sea squirts. These are very tough and hardy sharks, that can survive over a decade in captivity. The larger species should be treated with respect, as they will bite and clamp on to a human tormentor when provoked; and their vice-like jaws may need to be pried loose from a victim. One species (Ginglymostoma cirratum) has been indited in unprovoked attacks on people, but more often will bite when harassed.
Interest to Fisheries:
The larger species are common inshore sharks with wide ranges and are often caught in local inshore fisheries. They are utilized for human consumption, for liver oil, and for their thick and exceptionally tough hides, which make extremely good leather.
Remarks:
This family is recognized following the works of Compagno (1973c, 1982) and Applegate (1974). The genus Nebrius is sometimes considered a subgenus of Ginglymostoma as by Fowler (1941), but following Garman (1913), Whitley (1940), Bigelow and Schroeder (1948), Garrick and Schultz (1963), Applegate (1974), and Bass, d'Aubrey and Kistnasamy (1975b), it is accorded full generic status. Nebrius and Ginglymostoma are usually distinguished by tooth structural characters. According to Bigelow and Schroeder (1948), Ginglymostoma has teeth with the "central cusp" largest and with several series functional, while Nebrius has teeth with "all cusps equal" (cusps as large as cusplets) and with only one or two series functional. However, Nebrius material examined varied considerably in cusp size, but in no instance had the cusps only as large as the cusplets (cusps were smallest in young sharks, largest in adults); number of series functional ranged from 2 to 3 in Nebrius specimens but overlapped Ginglymostoma cirratum with 3 to 4. Hence the arrangement and definition of these genera are modified, and the two are distinguished by fin shape and tooth arrangement characters.
The small Ginglymostoma brevicaudatum is strongly divergent morphologically from G. cirratum, which is closer to Nebrius ferrugineus. Although G. brevicaudatum is clearly a ginglymostomatid, it differs from the other two species in having orthodont tooth structure, much smaller cusplets, larger cusps and narrower crowns on its teeth, smaller barbels, more posterior first dorsal origin, equal-sized dorsal fins, a shorter caudal fin, as well as cranial differences. This suggests that G. brevicaudatum may be generically distinct from Ginglymostoma proper, and may be referable to the fossil tooth genus Eostegostoma Herman and Crochard, 1977. G. cirratum is clearly intermediate between the more primitive G. brevicaudatum and the more derived N. ferrugineus. In cladistic terms, G. cirratum and N. ferrugineus are sister species, with G. brevicaudatum their primitive sister.