Mesoplodont whales are 16 species of toothed whale in the genus ''Mesoplodon'', making it the largest genus in the cetacean

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

. Two species were described as recently as 1991 (pygmy beaked whale) and 2002 (Perrin's beaked whale), and marine biologists predict the discovery of more species in the future. A new species was described in 2021. They are the most poorly known group of large mammals. The generic name "mesoplodon" comes from the Greek ''meso''- (middle) - ''hopla'' (arms) - ''odon'' (teeth), and may be translated as 'armed with a tooth in the centre of the jaw'.

Physical description

Scars from cookie-cutter shark bites on Gray's beaked whale

Mesoplodont beaked whales are small whales, (pygmy beaked whale) to (strap-toothed whale) in length, even compared with closely related whales such as the

bottlenose whale ''Hyperoodon'' (or ''Hyperoödon'') is a genus of beaked whale, containing just two species: the Northern and Southern bottlenose whales. While not in the genus ''Hyperoodon'', Longman's beaked whales are alternatively called tropical bottlenos ...

s and giant beaked whales. The spindle-shaped body has a small dorsal fin and short and narrow flippers. The head is small and tapered and has a semicircular blow hole that is sometimes asymmetric. The beak, which vary in length between species, blends with the small melon without a crease. Sexual dimorphism is poorly known, but the females tend to be the same size or larger than males at least in some species. The males typically have a bolder coloration and a unique dentition. The males of most species are covered in scars from the teeth of other males. The lower jaw often forms a huge arch in some species, sometimes extending above the rostrum in a shape comparable to a playground slide. Every species has large (sometimes tusk-like) teeth of variable size, shape, and position. Both sexes often have bites from

cookie-cutter shark The cookiecutter shark (''Isistius brasiliensis''), also called the cigar shark, is a species of small squaliform shark in the family Dalatiidae. This shark occurs in warm, oceanic waters worldwide, particularly near islands, and has been reco ...

s. The dorsal fin is rather small and located between two-thirds and three-quarters down the back of the animal. Information on longevity and lactation is non-existent, and information on gestation is nearly so.

Behavior

Most species are very rarely observed, and little is known about their behavior. They are typically found in groups, possibly segregated between sexes. Some species are so uncommon, they have yet to be observed alive. On the surface, they are typically very slow swimmers and do not make obvious blows. They have never been observed raising their flukes above the water. They are all very deep divers, and many feed entirely on squid.

Conservation

The mesoplodonts are completely unknown as far as population estimates are concerned. They have been hunted occasionally by the Japanese, but never directly. They are also accidentally captured in drift nets. It is not known what effect this has on the population.

Species

* Andrews' beaked whale (''M. bowdoini'') Andrews, 1908 *

Blainville's beaked whale Blainville's beaked whale (''Mesoplodon densirostris''), or the dense-beaked whale, is believed to be the widest ranging mesoplodont whale. The French zoologist Henri de Blainville first described the species in 1817 from a small piece of jaw � ...

(''M. densirostris'') Blainville, 1817 *

Deraniyagala's beaked whale Deraniyagala's beaked whale (''Mesoplodon hotaula'') is a species of mesoplodont whale. Taxonomy Deraniyagala's beaked whale was once synonymous with the Ginkgo-toothed beaked whale (''Mesoplodon ginkgodens''), until several studies confirmed t ...

(''M. hotaula'')

Deraniyagala Deraniyagala is a town in the Kegalle district in the Sabaragamuwa Province of Sri Lanka. Deraniyaga city area consists major government administrative offices, textile industries and transportation hub and the district hospital which has seve ...

, 1963 *

Gervais's beaked whale Gervais's beaked whale (''Mesoplodon europaeus''), sometimes known as the Antillean beaked whale, Gulf Stream beaked whale, or European beaked whale (from which its scientific name is derived) is the most frequently stranding type of mesoplodont ...

(''M. europaeus'') Gervais, 1855 *

Ginkgo-toothed beaked whale The ginkgo-toothed beaked whale (''Mesoplodon ginkgodens'') is a poorly known species of whale even for a beaked whale, and was named for the unusual shape of its dual teeth. It is a fairly typical-looking species, but is notable for the males no ...

(''M. ginkgodens'') Nishiwaki and Kamiya, 1958 *

Gray's beaked whale Gray's beaked whale (''Mesoplodon grayi''), sometimes known as Haast's beaked whale, the scamperdown whale, or the southern beaked whale, is one of the better-known members of the genus ''Mesoplodon''. This species is fairly gregarious and strand ...

(''M. grayi'') von Haast, 1876 * Hector's beaked whale (''M. hectori'') Gray, 1871 * Hubbs' beaked whale (''M. carlhubbsi'') Moore, 1963 * Perrin's beaked whale (''M. perrini'') Dalebout, Mead, Baker, Baker & van Helden, 2002 * Pygmy beaked whale (''M. peruvianus'') Reyes, Mead, and Van Waerebeek, 1991 * Sowerby's beaked whale (''M. bidens'') Sowerby, 1804 * Spade-toothed whale (''M. traversii'') Gray, 1874 * Stejneger's beaked whale (''M. stejnegeri'') True, 1885 * Strap-toothed whale (''M. layardii'') Gray, 1865 * True's beaked whale (''M. mirus'') True, 1913 * Ramari's beaked whale (''M. eueu'') Carroll ''et al'', 2021

Longman's beaked whale The tropical bottlenose whale (''Indopacetus pacificus''), also known as the Indo-Pacific beaked whale or Longman's beaked whale, was considered to be the world's rarest cetacean until recently, but the spade-toothed whale now holds that positio ...

(''Indopacetus pacificus'', also known as the Indo-Pacific beaked whale or the tropical bottlenose whale) was originally assigned to ''Mesoplodon'', but Joseph Curtis Moore placed it in its own genus, '' Indopacetus'', a taxonomic assignment which has been followed by all researchers. Three extinct species of ''Mesoplodon'' are known, ''M. posti'', ''M. slangkopi''. and ''M. tumidirostris''.Miyazaki, N.; Hasegawa, Y. 1992: A new species of fossil beaked whale, Mesoplodon tumidirostris sp. nov. (Cetacea, Ziphiidae) from the Central North Pacific. Bulletin of the National Science Museum (A), 18: 167–174. File:Mesoplodon bidens British mammals (Pl. 46) (21866206616).jpg, Sowerby's beaked whale, ''Mesoplodon bidens''; a male, with conspicuous teeth in the lower jaw File:Andrews' Beaked Whale (neonate, beachwashed) (cropped).JPG, A stranded newborn Andrews' Beaked Whale, ''M. bowdoini'' File:Hubbs' beaked whale skull.jpg, Skull of a Hubbs' beaked whale (''M. carlhubbsi'') File:Beaked Whale.jpg,

(''M. densirostris'') in the Bahamas File:Gervais' Beaked Whale.jpg,

(''M. europaeus'') in the

Gulf Stream The Gulf Stream, together with its northern extension the North Atlantic Current, North Atlantic Drift, is a warm and swift Atlantic Ocean, Atlantic ocean current that originates in the Gulf of Mexico and flows through the Straits of Florida a ...

off North Carolina File:Researchers conduct autopsy on stranded beaked whale.jpg, Autopsy of a stranded

(''M. grayi'') File:First underwater video of True's beaked whales underwater.ogv, True's beaked whale (''M. mirus'') off the Azores File:Mesoplodon traversii.svg, The Spade-toothed whale (''M. traversii'') was only morphologically described in 2012

References

Notes

Sources

* * *

External links

* Carly Cassella
Scientists Think They've Discovered a New Species of Beaked Whale
On: science^alert 12 December 2020 {{Taxonbar, from=Q243810 Ziphiids Taxa named by Paul Gervais Articles containing video clips