Carcharhiniformes, the ground sharks, are the largest order of sharks, with over 270 species. They include a number of common types, such as catsharks, swellsharks, and requiem sharks.
Members of this order are characterized by the presence of a nictitating membrane over the eye, two dorsal fins, an anal fin, and five gill slits.
The families in the order Carcharhiniformes are expected to be revised; recent DNA studies show that some of the conventional groups are not monophyletic.
The oldest members of the order appeared during the Middle-Late Jurassic, which have teeth and body forms that are morphologically similar to living catsharks.[1] Carchariniformes first underwent major diversification during the Late Cretaceous, initially as mostly small-sized forms, before radiating into medium and large body sizes during the Cenozoic.[2] [3]
According to FishBase, the nine families of ground sharks are:[4]
| Family | Image | Common name | Genera | Species | Description | |||||
|---|---|---|---|---|---|---|---|---|---|---|
| Carcharhinidae | align=center | Requiem sharks | align=center | 11 | align=center | 59 | valign=top | Requiem sharks are migratory, live-bearing sharks of warm seas (sometimes of brackish or fresh water) such as the blue shark, the bull shark, and the milk shark. The usual carcharhiniform characteristics include round eyes and pectoral fins that are completely behind five gill slits. Most species are viviparous, the young being born fully developed. They vary widely in size, from as small as 69cm (27inches) adult length in the Australian sharpnose shark, up to 4m (13feet) adult length in the oceanic whitetip shark.[5] Requiem sharks are responsible for a large proportion of attacks on humans. | ||
| †Florenceodontidae?[6] | align=center | align=center | 1 | align=center | 1 | valign=top | Extinct | |||
| Galeocerdonidae | align=center | Tiger shark | align=center | 1 | align=center | 1 extant | valign=top | A formerly diverse genus, only one species exists today. The tiger shark is the largest member of this order | ||
| Hemigaleidae | align=center | Weasel sharks | align=center | 4 | align=center | 8 | valign=top | Weasel sharks are found from the eastern Atlantic Ocean to the continental Indo-Pacific in shallow coastal waters to a depth of 100 m (330 ft). Most species are small, reaching no more than 1.4 m long (4.6 ft), though the snaggletooth shark (Hemipristis elongatus) may reach 2.4 m (7.9 ft). They have horizontally oval eyes, small spiracles, and precaudal pits. Two dorsal fins occur, with the base of the first placed well forward of the pelvic fins. The caudal fin has a strong ventral lobe and undulations on the dorsal lobe margin. They feed on a variety of small bony fishes and invertebrates; at least two species specialize on cephalopods. They are not known to have attacked people.[7] | ||
| Leptochariidae | align=center | Barbeled houndsharks | align=center | 1 | align=center | 1 | valign=top | The only species of barbeled houndshark is Leptocharias smithii. It is a demersal species found in the coastal waters of the eastern Atlantic Ocean from Mauritania to Angola, at depths of 10-. It favours muddy habitats, particularly around river mouths. The barbeled houndshark is characterized by a very slender body, nasal barbels, long furrows at the corners of the mouth, and sexually dimorphic teeth. Its maximum known length is 82cm (32inches). Likely strong-swimming and opportunistic, the barbeled houndshark has been known to ingest bony fishes, invertebrates, fish eggs, and even inedible objects. It is viviparous, with females bearing litters of seven young; the developing embryos are sustained by a unique globular placental structure. The IUCN has assessed the barbeled houndshark as near threatened, as heavy fishing pressure occurs throughout its range and it is used for meat and leather. | ||
| Proscylliidae | align=center | Finback catsharks | align=center | 3 | align=center | 7 | valign=top | |||
| Pseudotriakidae | align=center | False catsharks | align=center | 3 | align=center | 5 | valign=top | False catsharks are a small family containing false catsharks and gollumsharks. It contains the only ground shark species to exhibit intrauterine oophagy, in which developing fetuses are nourished by eggs produced by their mother. | ||
| †Pseudoscyliorhinidae | align=center | align=center | 2 | align=center | 3 | valign=top | Extinct | |||
| Scyliorhinidae | align=center | Catsharks | align=center | 17 | align=center | >150 | valign=top | Catsharks are distinguished by their elongated, cat-like eyes and two small dorsal fins set far back. They usually have a patterned appearance, ranging from stripes to patches to spots. Most are fairly small, growing no longer than 80cm (30inches); a few, such as the nursehound, can reach 1.6m (05.2feet) in length. They are found in temperate and tropical seas worldwide, ranging from shallow intertidal waters to depths of 2000m (7,000feet) or more, depending on species. They feed on invertebrates and smaller fish. Some species are aplacental viviparous, but most lay eggs in tough egg cases with curly tendrils at each end, known as mermaid's purses. The swell sharks of the genus Cephaloscyllium fill their stomachs with water or air when threatened, increasing their girth by a factor of two to three. Some catsharks are called dogfish. | ||
| Sphyrnidae | align=center | Hammerhead sharks | align=center | 2 | align=center | 9 | valign=top | Hammerhead sharks are named for the unusual and distinctive structure of their heads, which are flattened and laterally extended into a "hammer" shape called a cephalofoil. Many, not necessarily mutually exclusive, functions have been proposed for the cephalofoil, including sensory reception, manoeuvring, and prey manipulation. Hammerheads are found worldwide in warmer waters along coastlines and continental shelves. Unlike most sharks, hammerheads usually swim in schools during the day, becoming solitary hunters at night. | ||
| Triakidae | align=center | Houndsharks | align=center | 9 | align=center | 40 | valign=top | Houndsharks are distinguished by large spineless dorsal fins, an anal fin, and oval eyes with nictitating eyelids. They are small to medium in size, ranging from 37to in adult length. They are found throughout the world in warm and temperate waters, where they feed on fish and invertebrates on the sea bed and in midwater. |
The following fossil genera of Carcharhiniformes are also known:[8]
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