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The porbeagle has an almost global amphitemperate distribution, i.e.it is absent from the tropics; in the North Pacific, its niche is assumed by the salmon shark.Porbeagle populations in the Northern and Southern Hemispheres appear to be completely separate.There are two stocks in the North Atlantic, east and west, that seldom mix; only one individual is known to have crossed the Atlantic, covering 4,260 km (2,650 mi) from Ireland to Canada.Several discrete stocks are likely present in the Southern Hemisphere as well.This species segregates by size and sex in the North Atlantic, and at least by size in the South Pacific.However, Lamna teeth that closely resemble those of the porbeagle have been found in the La Meseta Formation on Seymour Island off the Antarctic Peninsula, which date to the middle to late Eocene epoch (50–34 Ma).There is much taxonomic confusion regarding Lamna in the fossil record due to the high degree of variability in adult tooth morphology within species.
The first scientific description of the porbeagle was authored by French naturalist Pierre Joseph Bonnaterre in the 1788 Tableau encyclopédique et methodique des trois règnes de la nature, and based on an earlier 1769 account by Welsh naturalist Thomas Pennant.
The porbeagle (Lamna nasus) is a species of mackerel shark in the family Lamnidae, distributed widely in the cold and temperate marine waters of the North Atlantic and Southern Hemisphere.
In the North Pacific, its ecological equivalent is the closely related salmon shark (L. The porbeagle typically reaches 2.5 m (8.2 ft) in length and a weight of 135 kg (298 lb); North Atlantic sharks grow larger than Southern Hemisphere sharks and differ in coloration and aspects of life history.
Bonnaterre named the shark Squalus nasus, the specific epithet nasus being Latin for "nose".
Several phylogenetic studies, based on morphological characters and mitochondrial DNA sequences, have established the sister species relationship between the porbeagle and the salmon shark (L. When its two extant species diverged from each other is uncertain, though the precipitating event was likely the formation of the ice cap over the Arctic Ocean, which would have isolated sharks in the North Pacific from those in the North Atlantic.