Megamouth shark

The first megamouth shark was captured on November 15, 1976, about 25 miles northeast of Kahuku, Hawaii, when it became entangled in the sea anchor of United States Navy research vessel AFB-14 of the Naval Undersea Center at a depth of about 165 m (541 ft). The species was identified as a new species and in its own family, Megachasmidae. Fossil records suggest that the species existed about 36 million years ago, while molecular studies date the species back further, as far back as 100 million years. Examination of the , specimen by Leighton Taylor showed it to be an entirely unknown type of shark, making it – along with the coelacanth – one of the more sensational discoveries in 20th-century ichthyology. The pectoral fin of the megamouth shark was studied, along with its skeletal and muscular system, to show its phylogenetic relationship to the other two planktivorous sharks. and possibly Vietnam. Researchers have predicted the feeding patterns of megamouth sharks in relation to the other two planktivorous sharks; the three planktivorous sharks have ram feeding in common, as it evolved from ram feeding swimming-type ancestors that developed their filtering mechanism to capture small prey like plankton. In addition to the living M. pelagios, however, two extinct megamouth species – the Priabonian M. alisonae and the Oligocene–Miocene M. applegatei – have also recently been proposed on the basis of fossilized tooth remains. An early ancestor of the recent species Megachasma pelagios was reported from the early Miocene (Burdigalian) of Belgium. However, the Cretaceous-aged M. comanchensis has been recently reclassified as an odontaspid shark in the genus Pseudomegachasma, and is in fact unrelated to the megamouth shark despite similar teeth morphology. The megamouth's filter-feeding adaptations likely evolved independently from other extant filter-feeding sharks, even the lamniform basking shark, making it an example of convergent evolution. ==Description==

, Japan, in 2016 The appearance of the megamouth is distinctive, but little else is known about it. It has a brownish-black colour on top, is white underneath, and has an asymmetrical tail with a long upper lobe, similar to that of the thresher shark. The interior of its gill slits are lined with finger-like gill rakers that capture its food. A relatively poor swimmer, the megamouth has a soft, flabby body and lacks caudal keels. The megamouth is considerably less active than the other filter-feeding sharks, the basking shark and the whale shark. The megamouth has a stout body and a long, wide bulbous head. Megamouths are large sharks, able to grow to in length. Mature males average at and females at . Weights of up to have been reported. A 2019 study suggested the megamouth may reach in maximum length. A 2024 study estimated that a male specimen caught off the coast of Ecuador in 2014 may have measured in total length, based on eyewitness accounts and the dimensions of the caudal fin. Megamouth sharks can be found as far northward as northern Japan; southern California (LACM 43745-1) and near Punta Eugenia, Baja California, and Hawaii. Megamouth sharks can be found at a depth of up to . This white band is present in both sexes and could be either a feeding mechanism or possibly be used as a means of identifying other individuals of megamouth sharks. Their mouths can reach up to in width. Megamouth sharks have up to 50 rows of teeth in their upper-jaw and up to 75 rows of teeth in their lower-jaw. The teeth of the megamouth shark are small and peg-like. == Behaviour ==

In 1990, a 4.9-m (16-foot) male megamouth shark was caught near the surface off Dana Point, California. This individual was eventually released with a small radio tag attached to its soft body. The tag relayed depth and time information over a two-day period. During the day, the shark swam at a depth around , but as the sun set, it would ascend and spend the night at depths between . Both day and night, its progress was very slow, around . In a 2024 study, three sharks were tagged off the coast of Taiwan and tracked over a multi-month period. The sharks reached a maximum depth from about 400–700 m (1310–2300 ft) during the day, on average. At night, they typically reached their minimum depth of 0–50 m (0–165 ft). This pattern of vertical migration is seen in many marine animals as they track the movement of plankton in the water column. Megamouth sharks undergo some seasonal migration as well, though this may be less consistent between individuals. While one shark migrated north from Taiwan during the summer, another migrated south. This revealed previously unknown social behaviors between individuals. Potential explanations for the behavior include foraging or mating, though neither behavior was specifically observed. ==Reproduction==

Reproduction is ovoviviparous, meaning that the young sharks develop in eggs that remain within the mother's body until they hatch. ==See also==