Smooth Hammerhead

The smooth hammerhead (Sphyrna zygaena) is a species of hammerhead shark, and part of the family Sphyrnidae. This species is named "smooth hammerhead" because of the distinctive shape of the head, which is flattened and laterally extended into a hammer shape (called the "cephalofoil"), without an indentation in the middle of the front margin (hence "smooth"). Unlike other hammerheads, this species prefers temperate waters and occurs worldwide at medium latitudes. In the summer, these sharks migrate towards the poles following cool water masses, sometimes forming schools numbering in the hundreds to thousands.
The second-largest hammerhead shark after the great hammerhead shark, the smooth hammerhead can measure up to 5 m (16 ft) long. It is an active predator that takes a wide variety of bony fishes and invertebrates, with larger individuals also feeding on sharks and rays. As in the rest of its family, this shark is viviparous and gives birth to litters of 20–40 pups. A relatively common shark, it is captured, intentionally or otherwise, by many commercial fisheries throughout its range; its fins are extremely valuable for use in shark fin soup. This shark is potentially dangerous and has likely been responsible for a few attacks on humans, though it is less likely to encounter swimmers than other large hammerhead species due to its temperate habitat.
== Description ==
The second-largest hammerhead next to the great hammerhead, the smooth hammerhead typically measures 2.5–3.5 m (8.2–11.5 ft) long, with a maximum recorded length and weight of 5 m (16 ft) and 400 kg (880 lb) respectively. The smooth hammerhead differs from other large hammerheads in the shape of its cephalofoil, which has a curved front margin without an indentation in the center. The cephalofoil is wide but short, measuring 26–29% of the body length across. The nostrils are located near the ends of the cephalofoil, with long grooves running towards the center. There are 26–32 tooth rows in the upper jaw and 25–30 tooth rows in the lower jaw. Each tooth is triangular in shape, with smooth to weakly serrated edges.
The body is streamlined, without a dorsal ridge between the two dorsal fins. The first dorsal fin is moderately tall and falcate (sickle-like) in shape, with a rounded tip. The pectoral and pelvic fins are not falcate, rather having nearly straight rear margins. The anal fin is larger than the second dorsal fin, with long free rear tip and a strong notch in the rear margin. The dermal denticles are densely packed, each with 5–7 horizontal ridges (3 in juveniles) leading to a W-shaped rear margin. The back is dark brownish gray to olive in color, in contrast to the simple brown of most other hammerheads, becoming lighter on the flanks. The belly is white, and sometimes the pectoral fins have dark edges underneath.
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