Description
The common thresher is a fairly robust shark with a torpedo-shaped trunk and a short, broad head. The dorsal profile of the head curves evenly down to the pointed, conical snout. The eyes are moderately large and lack nictitating membranes. The small mouth is arched and, unlike in other thresher sharks, has furrows at the corners. There are 32-53 upper and 25-50 lower tooth rows; the teeth are small, triangular, and smooth-edged, lacking lateral cusplets. The five pairs of gill slits are short, with the fourth and fifth pairs located over the pectoral fin bases.
The long, falcate (sickle-shaped) pectoral fins taper to narrowly pointed tips. The first dorsal fin is tall and positioned slightly closer to the pectoral fins than the pelvic fins. The pelvic fins are almost as large as the first dorsal fin and bear long, thin claspers in males. The second dorsal and anal fins are tiny, with the former positioned ahead of the latter. There are crescent-shaped notches on the caudal peduncle at the upper and lower origins of the caudal fin. The upper caudal fin lobe is enormously elongated as is characteristic of threshers, measuring about as long as the rest of the shark; the thin, gently curving lobe is held at a steep upward angle and has a notch in the trailing margin near the tip.
The skin is covered by small, overlapping dermal denticles, each with three horizontal ridges and three to five marginal teeth. This species is metallic purplish brown to gray above, becoming more bluish on the flanks. The underside is white, which extends over the pectoral and pelvic fin bases; this pattern is in contrast to the pelagic thresher, which is solidly colored over these fins. The meeting line between the dorsal and ventral coloration is often irregular. There may be a white spot at the tips of the pectoral fins. The common thresher is the largest thresher shark species, commonly reaching 5 m (16 ft) long and 230 kg (510 lb) in weight. The confirmed length record for this shark is 5.7 m (19 ft), while the maximum possible length may be 6.1–6.5 m (20–21 ft). The heaviest individual on record is a 4.8 m (16 ft) female that weighed 510 kg (1,100 lb).
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