Nature (IUCN) has assessed the porbeagle as vulnerable worldwide, and as either endangered or critically endangered in different parts of its northern range. Taxonomy The etymology of the word "porbeagle" is obscure. A common suggestion is that it combines "porpoise" and "beagle", referencing this shark's shape and tenacious hunting habits. Another is that it is derived from the Cornish porth, meaning "harbor", and bugel, meaning "shepherd". The Oxford English Dictionary states that the word was either borrowed from Cornish or formed from a Cornish first element with the English "beagle". The Dictionary also notes that no evidence exists for a connection to the French porc, meaning "swine", or to porpoise, as has been proposed. Other common names for the porbeagle include Atlantic mackerel shark, Beaumaris shark, bottle-nosed shark, and blue dog. 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. Bonnaterre named the shark Squalus nasus, the specific epithet nasus being Latin for "nose". In 1816, French naturalist Georges Cuvier placed the porbeagle into its own subgenus, Lamna, which later authors elevated to the rank of full genus. Phylogeny and evolution 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. ditropis), which occurs in place of it in the North Pacific. The genus Lamna evolved 65–45 Mya. 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. Fossilized porbeagle remains are known from Late Miocene epoch (about 7.2 Mya) deposits in Belgium and the Netherlands, Pliocene epoch (5.3–2.6 Mya) deposits in Belgium, Spain, and Chile, and Pleistocene epoch (2.6 Mya to 12,000 BP) deposits in the Netherlands. 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 Mya). Much taxonomic confusion remains regarding Lamna in the fossil record due to the high degree of variability in adult tooth morphology within species. Distribution and habitat The porbeagle