Editing Porbeagle (section)

==Description==
[[File:Lamna nasus csiro-nfc.jpg|thumb|upright=1.2|alt=Side view of a blue-gray shark|A Southern Hemisphere porbeagle showing the white patch on the rear tip of the first dorsal fin, which is unique to the species.]]
The porbeagle is a very stout-bodied shark with a fusiform (spindle-like) shape. The long, conical snout tapers to a sharp point, and is supported by enlarged, highly [[calcification|calcified]] [[wikt:rostral|rostral]] [[cartilage]]s. The eyes are large and black, without [[nictitating membrane]]s (protective third eyelids). The small, S-shaped [[nostril]]s are positioned in front of and below the level of the eyes. The mouth is large and strongly curved, with moderately protrusible jaws.<ref name="compagno"/> North Atlantic sharks have 28–29 upper tooth rows and 26–27 lower tooth rows, while Southern Hemisphere sharks have 30–31 upper tooth rows and 27–29 lower tooth rows.<ref name="last and stevens"/> Each tooth has a strongly arched base and a nearly straight, awl-like central cusp, which is flanked by a pair of smaller cusplets in all but the smallest individuals. The five pairs of [[gill slit]]s are long and precede the [[pectoral fin]] bases.<ref name="compagno"/>

The pectoral fins are long and narrow. The first dorsal fin is large and high, with a rounded apex, and originating just behind the pectoral fin bases. The [[pelvic fin]]s are much smaller than the first dorsal fin. The second dorsal and [[anal fin]]s are smaller still, and placed about even with each other on narrow bases that allow pivoting from side to side. The sides of the [[caudal peduncle]] are expanded into prominent lateral keels. A second, shorter pair of keels are present below the main keels. The [[caudal fin]] is large and crescent-shaped, with the lower lobe almost as long as the upper; both dorsal and ventral depressions (precaudal pits) are at the caudal fin base, and a deep ventral notch is near the tip of the upper caudal fin lobe.<ref name="compagno"/> The skin is soft and covered by tiny, flattened [[dermal denticle]]s ([[scale (zoology)|scales]]), lending a [[velvet]]y texture. Each denticle has three horizontal ridges that lead to teeth on the posterior margin.<ref name="roman"/>

The dorsal coloration is a medium to dark gray or slate, extending to the bases of the pectoral fins. The underside is white; adults in the Southern Hemisphere often have dark coloring under the head and dusky blotches scattered over the belly. The free rear tip of the first dorsal fin is abruptly light gray or white, a feature unique to this species. The porbeagle may attain a length of {{convert|3.7|m|ft|abbr=on}}, though this is uncertain and may have resulted from confusion with other mackerel shark species. A more typical length is {{convert|2.5|m|ft|abbr=on}}.<ref name="compagno"/><ref name="campana et al"/><ref name="fishbase"/> Female sharks grow larger than males in the North Atlantic, with maximum confirmed [[fork length]]s (snout tip to caudal fin fork) of {{convert|2.5|m|ft|abbr=on}} for males and {{convert|3.0|m|ft|abbr=on}} for females. Southern Hemisphere sharks are smaller and the two sexes are similar in size, with males and females attaining fork lengths of {{convert|2.0|and|2.1|m|ft|abbr=on}} respectively.<ref name="francis et al"/> Most porbeagles weigh no more than {{convert|135|kg|lb|abbr=on}}, with the record being a {{convert|230|kg|lb|abbr=on}} individual caught off [[Caithness]], [[Scotland]], in 1993.<ref name="compagno"/><ref name="martin"/>