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Species[edit]

Phocidae[edit]

Subfamily Phocinae[edit]

Tribe Phocini – 5 genera, 10 species
Genus Phoca Linnaeus, 1758 – two species
Common name Scientific name Subspecies Conservation status Threats Range Picture
Harbor seal
P. vitulina
Linnaeus, 1758
  • P. v. vitulina East Atlantic harbor seal LC IUCN; 62,500; Question?
  • P. v. concolor West Atlantic harbor seal LC IUCN; 60,000; Question?
  • P. v. mellonae Freshwater seal EN IUCN; 50; Question?
  • P. v. richardii North Pacific harbor seal LC IUCN; 190,000; Increase
  • P. v. stejnegeri Kuril Island seal DD IUCN; unknown; Question?
LC IUCN; 315,000; Question? Intentional hunting, natural causes, habitat destruction, accidental killing Leefgebied zeehond.JPG Seehund11cele4 edit.jpg
Spotted seal
P. largha
Pallas, 1811
LC IUCN; 320,000; Question? Habitat destruction, accidental killing, intentional hunting, climate change Spotted seal distribution in Bering Sea and surrounding areas.png Phoca largha Bering Sea 3.jpg
Genus Pusa Scopoli, 1771 – three species
Common name Scientific name Subspecies Conservation status Threats Range Picture
Ringed seal
P. hispida
von Schreber, 1775
  • P. h. hispida LC IUCN; 1,450,000; Question?
  • P. h. botnica Baltic seal LC IUCN; 11,500; Increase
  • P. h. ladogensis Ladoga seal VU IUCN; 3,000–4,500; Increase
  • P. h. ochotensis Okhosk ringed seal LC IUCN; 60,000; Question?
  • P. h. saimensis Saimaa ringed seal EN IUCN; 135–190; Increase
LC IUCN 1,500,000; Question? Climate change, habitat destruction, intentional hunting, accidental killing, natural causes
Phoca hispida distribution.png Pusa hispida hispida NOAA 1 (cropped).jpg
Caspian seal P. caspica
Gmelin, 1788
EN IUCN; 68,000; Question? Intentional hunting, accidental killing, natural causes, habitat destruction, climate change
Caspian Seal area.png Turkmenistani stamp
Baikal seal P. sibirica
Gmelin, 1788
LC IUCN; 54,000; Steady Intentional hunting, natural causes, habitat destruction, climate change Baikal Seal area.png Baikal seal 200507 hakone japan.JPG
Genus Histriophoca Zimmermann, 1783 – one species
Common name Scientific name Subspecies Conservation status Threats Range Picture
Ribbon seal H. fasciata
Zimmermann, 1783
LC IUCN; 183,000; Question? Intential hunting, accidental killing Phoca fasciata distribution.png Male Ribbon Sea Ozernoy Gulf Russia.jpg
Genus Pagophilus Erxleben, 1777 – one species
Common name Scientific name Subspecies Conservation status Threats Range Picture
Harp seal P. groenlandicus
Erxleben, 1777
LC IUCN; 4,500,000; Increase Intentional hunting, accidental killing, habitat destruction, climate change Sattelrobbe-Phoca groenlandica-World.png Harp seal at False Cape (cropped).jpg
Genus Halichoerus Fabricius, 1791 – one species
Common name Scientific name Subspecies Conservation status Threats Range Picture
Gray seal
H. grypus
Fabricius, 1791
  • H. g. grypus LC IUCN; 250,000; Increase
  • H. g. macrorhynchus LC IUCN; 66,000; Increase
LC IUCN; 316,000; Increase Intentional hunting, accidental killing, natural causes, habitat destruction Grey Seal Halichoerus grypus distribution map.png GreySealMating.jpg
Female left, male right
Genus Cystophora Erxleben, 1777 – one species
Common name Scientific name Subspecies Conservation status Threats Range Picture
Hooded seal C. cristata
Erxleben, 1777
VU IUCN; 340,000; Question? Intentonal hunting, accidental killing, habitat destruction, natural causes, climate change Klappmütze-Cystophora cristata-World.png Hooded seal crop.JPG
Genus Erignathus Erxleben, 1777 – one species
Common name Scientific name Subspecies Conservation status Threats Range Picture
Bearded seal E. barbatus
Erxleben, 1777
  • E. b. barbatus Atlantic bearded seal LC IUCN; >190,000[a]; Question?
  • E. b. nautilus Pacific bearded seal LC IUCN; 200,000; Question?
LC IUCN; unknown; Question? Climate change, habitat destruction, intentional hunting Erignathus barbatus distribution.png Seal by Christopher Michel.jpg

Subfamily Monachinae[edit]

Tribe Lobodontini – 4 genera, 4 species
Genus Leptonychotes Gill, 1872 – one species
Common name Scientific name Subspecies Conservation status Threats Range Picture
Weddell seal L. weddellii
Lesson, 1826
LC IUCN; 300,000; Question? Climate change, habitat destruction, intentional hunting Leefgebied weddell zeehond.JPG Weddell Seal (js)1 (cropped).jpg
Genus Hydrurga Gistel, 1848 – one species
Common name Scientific name Subspecies Conservation status Threats Range Picture
Leopard seal H. leptonyx
de Blainville, 1820
LC IUCN; 18,000; Question? Natural causes, climate change, habitat destruction Hydrurga leptonyx distribution.png Hydrurga leptonyx edit2.jpg
Genus Lobodon Gray, 1844 – one species
Common name Scientific name Subspecies Conservation status Threats Range Picture
Crabeater seal L. carcinophaga
Hombron and Jacquinot, 1842
LC IUCN; 4,000,000; Question? Natural causes, climate change Lobodon carcinophagus distribution.png Crabeater Seal in Pléneau Bay, Antarctica (6059168728).jpg
Genus Ommatophoca Gray, 1844 – one species
Common name Scientific name Subspecies Conservation status Threats Range Picture
Ross seal O. rossii
Gray, 1844
LC IUCN; 40,000; Question? Natural causes, climate change[b] Ross Seal area.png Rossrobbe.jpg
Tribe Miroungini – 1 genus, 2 species
Genus Mirounga Gray, 1827 – two species
Common name Scientific name Subspecies Conservation status Threats Range Picture
Southern elephant seal M. leonina
Linnaeus, 1758
LC IUCN; 325,000; Steady Intentional hunting, natural causes Southern Elephant Seal area.png
Male top, female bottom
Northern elephant seal M. angustirostris
Gill, 1866
LC IUCN; 110,000; Increase Intentional hunting, accidental killing, habitat destruction, natural causes Mirounga angustirostris distribution.png

Breeding range in dark blue

Mating scene with elevated Alpha Male. Elephant Seals of Piedras Blancas.jpg


Tribe Monachini – 2 genera, 3 species
Genus Monachus Fleming, 1822 – one species
Common name Scientific name Subspecies Conservation status Threats Range Picture
Mediterranean monk seal M. monachus
Hermann, 1799
EN IUCN; 350–450; Increase Intentional hunting, habitat destruction, accidental killing, natural causes Monachus monachus distribution.png Monachus monachus.jpg
Genus Neomonachus D.-M. Scheel et al., 2014 – two species
Common name Scientific name Subspecies Conservation status Threats Range Picture
Hawaiian monk seal N. schauinslandi
Matschie, 1905
EN IUCN; 632; Decrease Intentional hunting, accidental killing, habitat destruction, natural causes, climate change Hawaiian Monk Seal area.png Endangered Hawaiian monk seal sunning on the beach (6741931081).jpg
Caribbean monk seal
N. tropicalis
Gray, 1850
EX IUCN Extinct since 1952[c], intentional hunting, habitat destruction Middle America location map.svg Cms-newyorkzoologicalsociety1910.jpg

Otariidae[edit]

Arctocephalinae[edit]

Genus Arctocephalus Saint-Hilare and Cuvier, 1826 – eight species
Common name Scientific name Subspecies Conservation status Threats Range Picture
Antarctic fur seal A. gazella
Peters, 1875
LC IUCN; 700,000-1,000,000; Decrease Intentional hunting, accidental killing, habitat destruction, natural causes, climate change Antarctic Fur Seal area.png Antarctic, sea lion (js) 64.jpg
Guadalupe fur seal A. townsendi
Merriam, 1897
LC IUCN;[d] 10,000; Increase Intentional hunting, habitat destruction, climate change, natural causes Arctocephalus townsendi distribution.png
Breeding range in dark blue
Arctocephalus townsendi.jpg
Juan Fernández fur seal A. philippii
Peters, 1866
LC IUCN[e]; 16,000; Increase Intentional hunting, habitat destruction Juan Fernandez Fur Seal area.png Lobo fino.jpg
Galápagos fur seal A. galapagoensis
Heller, 1904
EN IUCN; 10,000; Decrease Intentional hunting, climate change Galapagos Fur Seal area.png Galapagos Fur Seal, Santiago Island.jpg
New Zealand Fur Seal A. forsteri
Lesson, 1828
LC IUCN; 100,000; Increase Intentional hunting, accidental killing, habitat destruction, natural causes Arctocephalus forsteri distribution.png Arctocephalus forsteri LC0255.jpg
Subantarctic fur seal
A. tropicalis Gray, 1872 LC IUCN; 200,000; Steady Intentional killing, climate change Subantarctic Fur Seal area.png Arctocephalus tropicalis CrozetIslands male.jpg
Brown fur seal A. pusillus
von Schreber, 1775
  • A. p. pusillus Cape fur seal LC IUCN; 1,000,000; Increase
  • A. p. doriferus Tasmanian fur seal LC IUCN; 60,000; Increase
LC IUCN; 1,060,000; Increase Intentional hunting, accidental killing, habitat destruction, climate change, natural causes Arctocephalus pusillus distribution.png
Breeding range in dark blue
Arctocephalus pusillus - SE Tasmania.jpg
South American fur seal A. australis
von Zimmermann, 1783
  • A. p. pusillus South American fur seal LC IUCN 99,000; Question?
  • Unnamed Peruvian fur seal VU IUCN 10,500; Question?
  • A. a. gracilis Falkland Island fur seal, unrecognized by IUCN
LC IUCN; 109,500; Increase Intentional hunting, habitat destruction, accidental killing Arctocephalus australis distribution.png Furseals1.jpg
Genus Callorhinus Gray, 1859 – one species
Common name Scientific name Subspecies Conservation status Threats Range Picture
Northern fur seal C. ursinus
Linnaeus, 1758
VU IUCN; 650,000; Decrease Intentional hunting, habitat destruction, natural causes Callorhinus ursinus distribution.png
Breeding range in dark blue
Alaska 2007 056.jpg

Otariinae[edit]

Genus Neophoca Gray, 1866 – one species
Common name Scientific name Subspecies Conservation status Threats Range Picture
Australian sea lion N. cinerea
Péron, 1816
EN IUCN; 6,500; Decrease Intentional hunting, accidental killing, habitat destruction, natural causes Neophoca cinerea distribution.png
Breeding range in dark blue
Neophoca cinerea.JPG
Genus Phocarctos Peters, 1866 – one species
Common name Scientific name Subspecies Conservation status Threats Range Picture
New Zealand sea lion P. hookeri
Gray, 1844
EN IUCN; 3,031; Decrease Intentional hunting, accidental killing, disease New Zealand Sea Lion area.png New Zealand Sea Lion, adult male.jpg
Genus Zalophus Gill, 1866 – three species
Common name Scientific name Subspecies Conservation status Threats Range Picture
California sea lion Z. californianus
Lesson, 1828
LC IUCN; 180,000; Increase Intentional hunting, habitat destruction, natural causes, climate change Zalophus californianus distribution.png
Breeding range in dark blue, Galápagos sea lion in red
Sea Lions Roar (18604860442).jpg
Galápagos sea lion Z. wollebaeki
Sivertsen, 1953
EN IUCN; 9,200–10,600; Decrease Climate change, habitat destruction, natural causes Galapagos Sea Lion area.png


Male top, female bottom

Japanese sea lion Z. japonicus
Peters, 1866
EX IUCN Extinct since 1951, intentional hunting Sea of Okhotsk map.png Zalophus japonicus.JPG
Genus Otaria Péron, 1816 – one species
Common name Scientific name Subspecies Conservation status Threats Range Picture
South American sea lion O. byronia[f]
de Blainville
LC IUCN; 222,500; Steady Habitat destruction, accidental killing, intentional hunting Otaria flavescens distribution.png Southern Sea Lions.jpg
Genus Eumetopias Gill, 1866 – one species
Common name Scientific name Subspecies Conservation status Threats Range Picture
Steller sea lion
E. jubatus
von Schreber, 1776
  • E. j. jubatus Western Steller sea lion LC IUCN; 40,409; Increase
  • E. j. monteriensis Eastern Steller sea lion LC IUCN; 40,919; Increase
NT IUCN; 81,327; Increase Intentional hunting, natural causes, habitat destruction Eumetopias jubatus distribution.png StellerSealionFamily.jpg

Odobenidae[edit]

Genus Odobenus Brisson, 1762 – one species
Common name Scientific name Subspecies Conservation status Threats Range Picture
Walrus O. rosmarus
Linnaeus, 1758
VU IUCN; 112,500; Question? Intentional hunting, habitat destruction, climate change Walross-Odobenus rosmarus-World.png Pacific Walrus - Bull (8247646168).jpg

Notes[edit]

  1. ^ 190,000 is the population in Canadian waters, but the population is unknown in Greenlandic and Norwegian waters
  2. ^ Not well-studied due to isolation
  3. ^ Current Caribbean reefs cannot support such a predator anymore, which indicates that the productivity of reef ecosystems has decreased due to overfishing.[1] However, another theory is that its pre-Columbia’s population was already low[2]
  4. ^ This species was declared extinct until 1954
  5. ^ This species was declared extinct until 1965
  6. ^ Listed as O. flavescens by Mammal Species of the World and ITIS

References[edit]

Extended content
Cryptodira – 11 families, 74 genera, over 200 species
Family[1] Genera[2]
Carettochelyidae
Boulenger, 1887 (1 genus)
Genus Carettochelys Ramsay, 1886 – one species
Common name Scientific name IUCN Red List Status Range Picture
Pig-nosed turtle C. insculpta
Ramsay, 1886
VU IUCN Southern New Guinea and northern Northern Territory
A beakless turtle with a snout shaped like that of a pigs
Cheloniidae (sea turtles)
Oppel, 1811 (5 genera)
Genus Caretta Rafinesque, 1814 – one species
Common name Scientific name IUCN Red List Status Range Picture
Loggerhead sea turtle C. caretta
Linnaeus, 1758
VU IUCN
World's oceans excluding the polar regions
A white turtle with a beak, black eye-spots, and a dark-brown carapace
Genus Lepidochelys (Ridley sea turtles) Fitzinger, 1843 – two species
Common name Scientific name IUCN Red List Status Range Picture
Kemp's ridley sea turtle L. kempii
Garman, 1880
CR IUCN
The Gulf of Mexico and the eastern coast of the United States
A green turtle with a white underside and beak
Olive ridley sea turtle L. olivacea
von Eschscholtz, 1829
VU IUCN
Coasts of Oceania, South China Sea, Sea of Japan, the Indian Ocean, Africa (excluding the Mediterranean), and the Americas (excluding the eastern coast of North America and southern South America)
alt=A green turtle with a white underside and beak
Genus Chelonia Brongniart, 1800 – one species
Common name Scientific name IUCN Red List Status Range Picture
Green sea turtle C. mydas
Linnaeus, 1758
EN IUCN
Tropical and temperate oceans of the world
A dark brown turtle with a beak, a green carapace, and a white underside
Genus Eretmochelys Fitzinger, 1843 – one species
Common name Scientific name IUCN Red List Status Range Picture
Hawksbill sea turtle E. imbricata
Linnaeus, 1758
CR IUCN
Tropical and subtropical oceans of the world
A turtle with a beak, a black head, flippers, and carapace, a white neck and underside, and serrated scutes on the carapace
Genus Natator McCulloch, 1908 – one species
Common name Scientific name IUCN Red List Status Range Picture
Flatback sea turtle N. depressus
Garman, 1880
DD IUCN
Around the coast of Australia, stretching to New Guinea and Java, excluding the southern coast
A grey turtle with a white beak
Chelydridae
Gray, 1831(2 genera)
Genus Chelydra (snapping turtles) Schweigger, 1812 – three species
Common name Scientific name IUCN Red List Status Range Picture
Common snapping turtle C. serpentina
Linnaeus, 1758
LC IUCN
United States east of the Rocky Mountains
An orange-brown tortoise with a grey carapace
Central American snapping turtle C. rossignonii
Bocourt, 1868
VU IUCN Southeastern Mexico, southern Belize, central Guatemala, and northwestern Honduras
Dermatemydidae
Gray, 1870 (1 genus)
Genus Dermatemys Gray, 1847 – one species
Common name Scientific name IUCN Red List Status Range Picture
Central American river turtle D. mawii
Gray, 1847
CR IUCN Eastern Mexico, Guatemala, Honduras, and Belize
A green turtle with webbed feet
Dermochelyidae
Fitzinger, 1843 (1 genus)
Genus Dermochelys de Blainville, 1816 – one species
Common name Scientific name IUCN Red List Status Range Picture
Leatherback sea turtle D. coriacea
Vandelli, 1761
VU IUCN
Oceans of the world
A large black turtle without a bony shell
Emydidae
Rafinesque, 1815 (12 genera)
Genus Clemmys von Ritgen, 1828 – one species
Common name Scientific name IUCN Red List Status Range Picture
Spotted turtle C. guttata
Schneider, 1792
EN IUCN Great Lakes region
A black tortoise with yellow speckles across the body and carapace
Genus Emys Duméril, 1805 – two species
Common name Scientific name IUCN Red List Status Range Picture
European pond turtle E. orbicularis
Linnaeus, 1758
EN IUCN
Mediterranean Europe, and around the Caspian Sea
A black tortoise with yellow speckles across the body and carapace
Sicilian pond turtle E. trinacris
Fritz, Fattizzo, Guicking, Tripepi, Pennisi, Lenk, Joger and Wink, 2005
DD IUCN
Sicily, an island off the coast of Italy
A grey tortoise
Genus Emydoidea Holbrook, 1838 – one species
Common name Scientific name IUCN Red List Status Range Picture
Blanding's turtle E. blandingii
Holbrook, 1838
EN IUCN
Great Lakes region in the United States
A black tortoise with yellow spots covering the body
Genus Actinemys Baird and Girard, 1852 – one species
Common name Scientific name IUCN Red List Status Range Picture
Western pond turtle A. marmorata
Baird and Girard, 1852
VU IUCN
Western coast of the contiguous United States
A dark brown turtle with webbed feet, and a yellow-speckled head and neck
Genus Glyptemys Agassiz, 1857 – two species
Common name Scientific name IUCN Red List Status Range Picture
Bog turtle G. muhlenbergii
Schoepff, 1801
CR IUCN
One population in New England and another population in Virginia, United States
A black turtle with an orange patch on its neck
Wood turtle G. insculpta
Le Conte, 1830
EN IUCN
New England, Newfoundland, and the Greats Lakes
A black tortoise with a yellow plastron and spots on the head and neck
Genus Terrapene (box turtles) Merrem, 1820 – four species
Common name Scientific name IUCN Red List Status Range Picture
Common box turtle T. carolina
Linnaeus, 1758
VU IUCN Eastern coast of North America, and the Gulf of Mexico
Eastern box turtle
T. c. carolina
Florida box turtle
T. c. bauri
Gulf Coast box turtle
T. c. major
Eastern box turtle.jpg Florida Box Turtle Digon3a.jpg Terrapene carolina major.jpg
Three-toed box turtle
T. c. triunguis
Mexican box turtle
T. c. mexicana
Yucatán box turtle
T. c. yucatana
Three-toed Box Turtle.jpg CistudoMexicanaFord.jpg Terrapene carolina yucatana.jpg
Coahuilan box turtle T. coahuila
Schmidt and Owens, 1944
EN IUCN Cuatro Ciénegas, Coahuila, Mexico A dark grey tortoise
Spotted box turtle T. nelsoni
Stejneger, 1925
DD IUCN Sierra Madre Occidental, Mexico
Terrapene ornata] Terrapene ornata
Agassiz, 1857
NT IUCN Central United States, including the Mojave desert and the Midwest region Brown tortoises
Ornate box turtle left, Desert box turtle right
Genus Chrysemys Gray, 1844 – one species
Common name Scientific name IUCN Red List Status Range Picture
Painted turtle C. picta
Schneider, 1783
LC IUCN
United States spilling over into Canada excluding the Mojave desert
Eastern painted turtle
C. p. picta
Midland painted turtle
C. p. marginata
Southern painted turtle
C. p. dorsalis
Western painted turtle
C. p. bellii
A grey tortoise with square patterns on the carapace A brown tortoise A grey tortoise with a single thin, orange line running down the carapace from head to tail and white marks on the head and neck A grey tortoise with yellow stripes running down the neck from the head
Underside view, showing a tan plastron Underside view, showing a tan plastron Underside view, showing a tan plastron and webbed feet Underside view, the plastron is bright red with black and white Rorshach-like patterns
Geoemydidae
Theobald, 1868
24
Kinosternidae
Agassiz, 1857
4
Platysternidae
Gray, 1869
1
Testudinidae
Batsch, 1788
12
Trionychidae
Fitzinger, 1826
14
Pleurodira – 3 families, 16 genera, over 60 species
Family Genera
Chelidae
Gray, 1831
15
Pelomedusidae
Cope, 1868
2
Podocnemididae
Gray, 1869
3

References

  1. ^ John B. Iverson; A. Jon Kimerling; A. Ross Kiester. "List of All Families". Terra Cognita Laboratory, Geosciences Department of Oregon State University. Retrieved 26 June 2010.
  2. ^ John B. Iverson; A. Jon Kimerling; A. Ross Kiester. "List of Genera". Terra Cognita Laboratory, Geosciences Department of Oregon State University. Retrieved 26 June 2010.

Further reading

  • David T. Kirkpatrick (November–December 1995). "Platysternon megacephalum". Reptile & Amphibian Magazine. pp. 40–47. Retrieved 26 June 2010.
  • Cogger, H.G.; R.G. Zweifel; D. Kirschner (2004). Encyclopedia of Reptiles & Amphibians Second Edition. Fog City Press. ISBN 1-877019-69-0.

External links

  • John B. Iverson; A. Jon Kimerling; A. Ross Kiester. "EMYSystems". Terra Cognita Laboratory, Geosciences Department of Oregon State University. Retrieved 26 June 2010.
Extended content

Cetacean anatomy is the study of the form or morphology of cetaceans (whales, dolphins and porpoises). It can be contrasted with cetacean physiology, which is the study of how the component parts of cetaceans function together in these living marine mammals.[1] In practice, cetacean anatomy and cetacean physiology complement each other, the former dealing with the structure of a cetacean, its organs or component parts and how they are put together, such as might be observed on the dissecting table or under the microscope, and the latter dealing with how those components function together in the living marine mammal.

The anatomy of cetaceans have common characteristics with other terrestrial mammals, and, in addition, is often shaped by the physical characteristics of aquatic living, the medium in which these mammals live. Water is much denser than air, holds a relatively small amount of dissolved oxygen, and absorbs more light than air does.

Body

Skeleton Skull

Unlike toothed whales (left), baleen whales (right) do not have a melon

The skull of all cetaceans is extended, which can be clearly seen in baleen whales. The nostrils are located on top of the head above the eyes. The back of the skull is significantly shortened and deformed. By shifting the nostrils to the top of the head, the nasal passages extend perpendicularly through the skull. The teeth or baleen in the upper jaw sit exclusively on the maxilla. The braincase is concentrated through the nasal passage to the front and is correspondingly higher, with individual cranial bones that overlap. The bony otic capsule, the petrosal, is only cartilaginous when connected to the skull, so that it can swing independently.[2][3]

Vertebrae

The number of vertebrae that make up the spine varies between species, anywhere between 40 and 93 individual vertebrae. The cervical spine, found in all mammals, consists of seven vertebrae which, however, are greatly reduced or fused together. This gives stability during swimming at the expense of mobility. The fins are carried by the thoracic vertebrae, ranging from 9 to 17 individual vertebrae. The sternum is only cartilaginous, but nonetheless strong. The last two to three pairs of ribs are not connected at all and hang freely in the body wall. Behind it is the stable lumbar and tail part of the spine which includes all other vertebrae. Below the caudal vertebrae is the chevron bone; the vortex developed provides additional attachment points for the tail musculature.[2][3]

Limbs

The front limbs are paddle-shaped with shortened arms and elongated finger bones, to support the movement. They are united by cartilage. It also leads to a proliferation of the finger members, a so-called hyperphalangy, on the second and third fingers. The only functional joint is the shoulder joint in all cetaceans except for the Amazon river dolphin. The collarbone is completely absent. The movement of cetaceans on land is no longer necessary nor possible, due to the great body weight and the atrophied hindlimbs. In fact the rear limbs have become a rudimentary internal appendage without connections to the spine.[2][3]

External organs Jaw

The jaws of toothed whales are designed for catching swift prey. Porpoises have spade-shaped teeth, but dolphins have conical teeth. Cetaceans are monophydonts, meaning they have one set of teeth their entire life.[4] Toothed whales use their jaw to recieve pulses for echolocation. Echoes are received using complex fatty structures around the lower jaw as the primary reception path, from where they are transmitted to the middle ear via a continuous fat body.[5] Lateral sound may be received though fatty lobes surrounding the ears with a similar density to water. Some researchers believe that when they approach the object of interest, they protect themselves against the louder echo by quieting the emitted sound. This is known to happen in bats, but here the hearing sensitivity is also reduced close to a target.[6]

As opposed to toothed whales, baleen whales have different jaw designs depending on their feeding behaviour. Lunge-feeders, like rorquals, have to expand their jaw to a volume that can be bigger than the whale itself; to do this, the oral cavity inflates to expand the mouth. The inflation of the oral cavity causes the cavum ventrale, the folds (throat pleats) on the throat stretching to the naval, to expand, increasing the amount of water that the mouth can store.[7] The mandible is connected to the skull by dense fibers and cartilage, allowing the jaw to swing open at almost a 90° angle. The mandibular symphysis is also fibrocartilaginous, allowing the jaw to bend which lets in more water.[8] To prevent stretching the mouth too far, rorquals have a sensory organ located in the middle of the jaw to regulate these functions.[9] Gulp-feeders, like right whales, on the other hand swim with an open mouth, filling it with water and prey. This makes their head, which can make up a third of their body weight, huge in order to feed effectively. Not able to expand their mouth like rorquals, right whales must have a head that is large enough to take in enough water and food to feed effectively, carrying their bulk all the time.[10]

Beaked whales have a somewhat similar jaw anatomy as rorquals. The throats of beaked whales have a bilaterally paired set of grooves that are associated with their unique feeding mechanism, suction feeding. Instead of capturing prey with their teeth, beaked whales suck it into their oral cavity. Suction is aided by the throat grooves, which stretch and expand to accommodate food. Their tongue can move very freely. By suddenly retracting the tongue and distending the gular (throat) floor, pressure immediately drops within the mouth sucking the prey in with the water.[11]

Eyes The whale eye is relatively small for its size, yet they do retain a good degree of eyesight. As well as this, the eyes of a whale are placed on the sides of its head, so their vision consists of two fields, rather than a binocular view like humans have. When belugas surface, their lens and cornea correct the nearsightedness that results from the refraction of light; they contain both rod and cone cells, meaning they can see in both dim and bright light, but they have far more rod cells than they do cone cells. Whales do, however, lack short wavelength sensitive visual pigments in their cone cells indicating a more limited capacity for colour vision than most mammals.[12] Most whales have slightly flattened eyeballs, enlarged pupils (which shrink as they surface to prevent damage), slightly flattened corneas and a tapetum lucidum; these adaptations allow for large amounts of light to pass through the eye and, therefore, a very clear image of the surrounding area. In water, a whale can see around 10.7 metres (35 ft) ahead of itself, but, of course, they have a smaller range above water. They also have glands on the eyelids and outer corneal layer that act as protection for the cornea.[13] Toothed whales can retract and protrude its eyes thanks to a 2-cm-thick retractor muscle attached around the eye at the equator.[14]

Blowhole

The blowhole is the hole at the top of a whale's head through which the animal breathes air. When a whale reaches the water surface to breathe, they will forcefully expel air through the blowhole. Mucus and carbon dioxide from the animal's metabolism, which have been stored in the whale while diving, are also expelled. The exhalation is released into the comparably lower-pressure and colder atmosphere, so any water vapor condenses. This spray, known as the blow, is often visible from far away as a white splash, which can also be caused by water resting on top of the blowhole. Baleen whales have two blowholes, causing a V-shaped blow, while toothed whales have only one blowhole. The trachea only connects to the blowhole and there is no connection to the esophagus as with humans and most other mammals. Because of this, there is no risk of food accidentally ending up in the animal's lungs, and likewise the animal cannot breathe through its mouth. Consequently, whales have no pharyngeal reflex.[15]

Skin

Fins

Internal organs

Intestines The small intestines is divided into three sections: the duodenum, the jejunum, and the ileum. The mesentery is thin in baleen whales. The caecum is present in all whales with the exception of the Amazon river dolphins and the right whales, however it is relatively short in baleen whales. The appendix is absent in all cetaceans.

Stomach In most whales, food is swallowed and travels down through the esophagus where it meets a three-chambered-stomach. The first compartment is known as the fore-stomach; this is where food gets ground up into an acidic liquid, which is then squirted into the main stomach. Like in humans, the food is mixed with hydrochloric acid and protein-digesting enzymes. Then, the partly digested food is moved into the third stomach, in which fat-digesting enzymes, and then mixed with an alkaline liquid to neutralize the acid from the first stomach to prevent damage to the intestinal tract. Once the solution is safe, it is moved into the intestinal tract.

Kidneys Whale kidneys are specially designed for excreting excess salt content. Water is typically gained by the food they eat, however, the invertebrates they consume have the same salt content as seawater. As in other vertebrates, whale salt levels are three times less than that of seawater. However, the kidneys are inefficient at retaining water, and expel much of it while excreting salt.[16]

Spleen Liver The liver in whales is bilobed, as opposed to the five-lobed liver in humans, and they lack a gall bladder. Toothed whales have one bile duct and baleen whales have two. Like other mammals, the liver is located in the right side of the body, just below the diaphragm.

Heart

Swim bladder Weberian apparatus

Reproductive organs Testes Ovaries

Nervous system Central nervous system Cerebellum Identified neurons Immune system

See also

References

  1. ^ Prosser, C. Ladd (1991). Comparative Animal Physiology, Environmental and Metabolic Animal Physiology (4th ed.). Hoboken, NJ: Wiley-Liss. pp. 1–12. ISBN 0-471-85767-X.
  2. ^ a b c Bruno Cozzi; Sandro Mazzariol; Michela Podestà; Alessandro Zott (2009). "Diving Adaptations of the Cetacean Skeleton" (PDF). The Open Zoology Journal. 2: 24–32. doi:10.2174/1874336600902010024. Retrieved 5 September 2015.
  3. ^ a b c A. Thomas, J. (1916). Outlines of Zoology (5 ed.). pp. 766–771.
  4. ^ The Institute for Marine Mammal Studies. "Frequently asked questions". IMMS. Retrieved 17 February 2016.
  5. ^ Webster, D.; Fay, R.; Popper, A. (1992). "The Marine Mammal Ear: Specializations for aquatic audition and echolocation". In Ketten, D.R. (ed.). The Evolutionary Biology of Hearing. Springer-Verlag. pp. 717–750. ISBN 978-1-4612-7668-5.
  6. ^ Au, W.; Fay, R.; Popper, A. (2000). "Cetacean Ears". Hearing by Whales and Dolphins. SHAR Series for Auditory Research. Springer-Verlag. pp. 43–108. doi:10.1007/978-1-4612-1150-1. ISBN 978-0-387-94906-2.
  7. ^ W. Vogle, A.; A. Lillie, Margo; A. Piscitelli, Marina; A. Goldbogen, Jeremy; D. Pyenson, Nicholas; E. Shadwick, Robert (2015). "Stretchy nerves are an essential component of the extreme feeding mechanism of rorqual whales". Current Biology. 25 (9): 360–361. doi:10.1016/j.cub.2015.03.007.
  8. ^ A. Goldbogen, Jeremy (2010). "The Ultimate Mouthful: Lunge Feeding in Rorqual Whales". American Scientist. 98 (2): 124. doi:10.1511/2010.83.124.
  9. ^ Welsh, Jennifer (2012). "Whale's Big Gulp Aided by Newfound Organ". Retrieved 23 January 2016.
  10. ^ Kenney, Robert D. (2002). "North Atlantic, North Pacific and Southern Right Whales". In William F. Perrin, Bernd Wursig and J. G. M. Thewissen (ed.). The Encyclopedia of Marine Mammals. Academic Press. pp. 806–813. ISBN 0-12-551340-2.
  11. ^ Rommel, S. A.; Costidis, A. M.; Fernandez, A.; Jepson, P. D.; Pabst, D. A.; McLellan, W. A.; Houser, D. S.; Cranford, T. W.; van Helden, A. L.; Allen, D. M.; Barros, N. B. (2006). "Elements of beaked whale anatomy and diving physiology and some hypothetical causes of sonar-related stranding". Journal of Cetacean Research and Management. 7 (3): 189–209.
  12. ^ Mass et al. 2007, pp. 701–715.
  13. ^ Reidenberg, Joy S. (2007). "Anatomical adaptations of aquatic mammals". The Anatomical Record. 290 (6): 507–513. doi:10.1002/ar.20541.
  14. ^ Bjerager, P.; Heegaard, S.; Tougaar, J. (2003). "Anatomy of the eye of the sperm whale (Physeter macrocephalus L.)". Aquatic Mammals. 29 (1): 31–36. doi:10.1578/016754203101024059.
  15. ^ Tinker 1988, The Respiratory System, pp.65–68.
  16. ^ Cavendish, Marshall (2010). "Gray whale". Mammal Anatomy: An Illustrated Guide. ISBN 978-0-7614-7882-9.

Further reading

Extended content

Species

Baleen whaleS

There are 14 recognized species of baleen whales: Antarctic minke whale, the blue whale, bowhead whale, Bryde's whale, common minke whale, fin whale, gray whale, humpback whale, northern right whale, Omura's whale, pygmy right whale, sei whale, and southern right whale.[1]

Species Description Image
Blue whale (Balaenoptera musculus) status EN The blue whale is the largest animal that ever lived on Earth, much larger than the largest dinosaur. This whale has been extensively hunted in the past. Between 1930 and 1971, about 280,000 blue whales have been killed. In 1966, when it became obvious not many blue whales were left, the International Whaling Commission (IWC) declared the blue whale a protected species. Blue whales produce very low frequency sounds (even below 20 Hz), which can be detected over large distances.[2] Average length is 24 to 27 m (79 to 89 ft). The largest whale found was 33.58 m (110.2 ft) long. Females are larger than males. Typical weight is 100 to 120 metric tons (110 to 130 short tons), up to 190 metric tons (210 short tons). Average age is 70 to 90 years. The skin is blue-grey coloured, mottled with grey-white. The large body is very broad. There is a large ridge on the head leading from the tip of the snout to the blowholes. The region of the blowholes is raised. A very small dorsal fin is located about 25% of the length in front of the tail flukes. The flippers are long and thin. The tail flukes are relatively small. There are 55–88 grooves extending from the chin to the navel. These grooves allow the mouth to extend considerably during feeding. The tongue, palate and baleen are black. The baleen is wide and relatively short (less than 1 metre (3.3 ft) in length). While it has a worldwide distribution, it feeds in polar waters in summer and spends the winter in tropical and subtropical waters. Blue whales usually swim alone or in groups of two or three animals. They may group together on feeding grounds and form mixed-species groups with fin whales. The blue whale feeds almost exclusively on krill, rarely on small fish, such as capelin and sardines. Blue whales are rorquals, meaning they have long throat pleats that extend from the mouth to the naval; these skin flaps allow the whales mouth to expand so it can take in water, and sift through the krill and plankton within it, more efficiently.[3] Abundance: probably about 11,200 worldwide. In the North Atlantic there are only a few hundred blue whales left. Although the numbers are increasing, the blue whale is still endangered.[4][5][6] Blue whale
Bowhead whale (Balaena mysticetus) status LC The bowhead whale was a target of early whaling operations. It was hunted for its oil and baleen. The Inuit people occasionally take a few whales in the Bering/Chukchi/Beaufort Sea area.[7] Typical length is 14 to 18 metres (46 to 59 ft). Females are slightly larger than males. Average weight is 60 to 90 metric tons (66 to 99 short tons). Average age is 100 to 200 years, making it one of the longest-lived creatures alive today. The bowhead whale is a very stocky animal with a large head. The mouth is bowed strongly upward. The skin is smooth and free of parasites. They are blue-black in colour with random light patches on the stomach and lower jaw. There is no dorsal fin. The flippers are relatively small and paddle-shaped. The tail flukes are wide and pointed. The baleen plates are narrow (30 cm) and very long, up to 4.3 metres (14 ft). Its lives in Arctic waters, near pack ice. There are three main bowhead whale areas: Spitsbergen, Davis Strait, Okhotsk Sea and Bering/Chukchi/Beaufort Sea. Usually the bowhead is seen alone or in small groups of up to three individuals. It feeds on small crustaceans. Bowhead whales are balaenids, meaning they use their massive baleen plates, which are the largest (4.5 metres (15 ft)), to take in water; balaenids lack throat pleets, but they make up for it in head size which makes up around 40% of their body mass.[8] The Bering/Chukchi/Beaufort Sea has about 7,800 individuals. The Spitsbergen stock is probably extinct and the populations in the other areas have probably only a few hundred individuals.[4][5][6] Bowhead whale
Bryde's whale (Balaenoptera edeni)
status DD
Bryde's whale is easily confused with the sei whale. At close range, Bryde's whale can be easily recognised by the three parallel ridges on the head. The sei whale has only one central ridge. Bryde's whale is known to breach often in some areas. Bryde's whale is the least hunted of the rorqual species, mainly because it inhabits tropical and subtropical waters that were closed to whaling operations, because other species had been depleted in the area.[9] Average length is 11.5 to 14.5 metres (38 to 48 ft) and average weight is 10 to 20 metric tons (11 to 22 short tons). Females can live up to 52 years of age and males up to 55 years of age. Bryde's whale has 3 ridges on the head leading from the tip of the upper jaw to the blowholes. The Bryde's whale is dark grey on the back and lighter on the belly. They sometimes have light oval scars, caused by cookiecutter sharks. The dorsal fin is small and very curved. The flippers are medium-sized and thin, and somewhat rounded at the tip. The tail flukes are almost identical to those of the blue whale. It inhabits tropical and subtropical waters, between 40N and 40S latitude. It is usually alone or in groups of up to 10. They feed mainly on schooling fish, crustaceans and squid. Bryde's whales are rorquals, meaning they have long throat pleats that extend from the mouth to the naval; these skin flaps allow the whales mouth to expand so it can take in water, and sift through the krill and plankton within it, more efficiently.[3] The North Pacific population is probably about 20,000–30,000 individuals. Not much is known about other areas.[4][5] Bryde's whale
Fin whale (Balaenoptera physalus) status EN The fin whale is a fast swimmer, reaching speeds of 47 km/hr. It occasionally jumps clear of the water but does so less than other rorquals. They hardly ever show their tails before diving deep.[10] Size is 18 to 22 metres (59 to 72 ft), up to 27 metres (89 ft). Females are larger than males. Northern Hemisphere fin whales are on average 1 12 metres (4.9 ft) shorter than Southern Hemisphere fin whales. Average age is 60 to 100 years. Weight ranges from 30 to 75 metric tons (33 to 83 short tons). The fin whale is a long and slender whale. The head resembles that of the blue whale. The fin whale is dark grey to brown in colour, with flanks that lighten towards the belly. The dark colour extends farther down on the left side than on the right. Most animals have a light chevron just behind the head. The large dorsal fin (60 cm high) is placed far back. The flippers are thin and pointed. The tail flukes are large, thin and pointed and look like blue whale flukes. It has a worldwide distribution, in deeper water. It is usually found in groups of up to 10, but larger groups (up to 100) are not uncommon. Its diet is mainly small crustaceans, but Northern Hemisphere fin whales also feed on fish. Fin whales are rorquals, meaning they have long throat pleats that extend from the mouth to the naval; these skin flaps allow the whales mouth to expand so it can take in water, and sift through the krill and plankton within it, more efficiently. They've been seen herding fish into bait balls before engulfing them.[3][11] There are roughly 100,000 in the Southern Hemisphere, but only 30,000 in the Northern Hemisphere, split two to one between the North Pacific and the North Atlantic.[4][5][6] Fin whale
Gray whale (Eschrichtius robustus) status LC The gray whale spends the winter in the lagoons of Baja California, Mexico. In summer they move to Alaska to feed. They travel along the US coast and the grey whale migration can be seen from several land-based spots along the coast. The gray whale is one of the few species who have come back from the brink of extinction. After a period of intense whaling, the species was nearly extinct, but it has recovered to the point that the US has taken it off its endangered species list. This species is 13.5 to 15 metres (44 to 49 ft) in length and weighs up to 27 metric tons (30 short tons). Average age is 50 to 70 years. The grey whale is mottled grey all over. The skin on the back has large yellow and white coloured patches caused by parasites like barnacle and whale lice . The mouth is slightly bowed. They have more bristles on the tips of their upper and lower jaws than any other whale species. The grey whale has no dorsal fin but a number of bumps on the back and tail stock. The flippers are large and paddle-shaped. The baleen plates are yellowish and about 40 cm long, with long, thick bristles. It resides in the North Pacific only. The gray whale used to be present in the North Atlantic as well, but is now extinct there. In summer, they feed in the northern Bering Sea. During migration, females with calves swim together in groups of about 6 adults. Later in the migration, there are groups of three to five non-pregnant females with one or two males. The last on the migration are juvenile animals. The gray whale feeds on the bottom. The prey consists of crustaceans, molluscs and small fish. Grey whales are bottom feeders, meaning they dive down to the ocean floor and suck up the sediment; they then sift through the sediment for their prey. The Eastern population is probably about 21,000 individuals and is increasing in size at about 3.2% per year. The Western Pacific population is small, probably 100-200 individuals.[4][5][6] Gray whale
Humpback whale (Megaptera novaeangliae) status LC The humpback whale is probably one of the best known baleen whale species. The humpback whale is famous for its songs, of which even records have been made. The function of the songs is not clear. Most likely, the songs play a role in territorial behavior and in courting. Only the males sing. These songs can be heard over large distances. Humpback whales have developed a unique way of catching fish: they dive down, then slowly circle to the surface, blowing bubbles on the way up. This will encircle the fish in a net of bubbles. The whales then surface with open mouths in the middle of the circle, gulping up the concentrated fish. Humpback whales migrate over large distances. In the North Pacific, Humpbacks spend the winter near Hawaii or Baja Californian and in summer, move to Alaska to feed.[12] This species is up to 19 metres (62 ft) long and weighs up to 48 metric tons (53 short tons). Average age is 40 to 100 years. The humpback whale is black all over, with very long flippers, which vary in colour from black to white. There are also lighter patches on the belly and chest. The underside of the tail flukes also have patterns, which are unique for each individual. From the blowhole to the tip of the snout and laterally towards the edges of the mouth there are conspicuous hair follicles on large bumps. The dorsal fin is small and set far back (about 2/3 of the body length). Its distribution is worldwide, but they follow fixed migration patterns. In the summer, they feed in the polar regions and they migrate to warmer waters in the winter for breeding. There are three isolated populations: North Pacific, North Atlantic and Southern Hemisphere. On the calving grounds, they usually form groups of about 10-12. During migration they travel in groups of three to four. They feed on krill, plankton, and small schooling fish. Humpback whales are rorquals, meaning they have long throat pleats that extend from the mouth to the naval; these skin flaps allow the whales mouth to expand so it can take in water, and sift through the krill and plankton within it, more efficiently.[3] There are about 5,500 in the North Atlantic, 2,500 in the North Pacific and about 12,000 in the Southern Hemisphere. There may also be a resident population of about 500 individuals in the Indian Ocean. The humpback whale is considered to be a vulnerable species.[4][5][6] Humpback whale
Minke whale (Balaenoptera acutorostrata, Balaenoptera bonaerensis) status LC The minke whale became the target of whaling operations when the larger whales had declined to a level that made hunting them commercially unattractive. With all the larger whales reduced in numbers, the minke whales could multiply. Commercial fisheries for minke whales has restarted in Norway. In 1996, Norwegian whalers took 116 minke whales and in 1997, 503. In Greenland, the indigenous people are allowed to take 465 minke whales in 2 years.[13] This whale species is 7 to 10 metres (23 to 33 ft), making it the smallest of the baleen whales. Average age is 30 to 50 years. They weigh 4.5 to 9 metric tons (5.0 to 9.9 short tons). The snout is pointed, and there is a clear under-bite. The back is black, whereas the belly region is white. They have a distinctive white band on the long, thin flippers. They have a well-developed curved dorsal fin, which looks like the dorsal fin of the bottlenose dolphin. Most Pacific animals have a light chevron on their flanks. It prefers temperate waters, around the world. They are usually found in small groups of 6 or less. They feed mainly on shoaling fish, and also on krill and plankton. Minke whales are rorquals, meaning they have long throat pleats that extend from the mouth to the naval; these skin flaps allow the whales mouth to expand so it can take in water, and sift through the krill and plankton within it, more efficiently.[3] In the North Pacific (B. acutorostrata) there are 18,000-27,000, in the Northeastern Atlantic (B. acutorostrata): 90-135,000, in the Central Atlantic (B. acutorostrata) about 60,000, and in the Southern Hemisphere (B. bonaerensis) 200-400,000.[4][5][6][14] Common minke whale
Omura's whale (Balaenoptera omurai)
status DD
Omura's whale, sometimes referred to as the dwarf fin whale, is a very mysterious type of whale. Prior to 2003, omura's whale was thought to be a dwarf variation of bryde's whale, and as a result, very little is known about them. This species was originally identified by only ten or so individuals. Their colouration has been reported in some individuals to resemble the fin whale, hence its nickname. Males reach a length of a mere 8.2 to 10.1 metres (27 to 33 ft), and females reach 9.8 to 11.5 metres (32 to 38 ft), making Omura's whale one of the smallest baleen whales. Their average weight remains unknown, as well as their average age.[15] Based on sightings, they are thought to travel alone and, rarely, in pairs. Since they are rorquals, they are believed to feed predominately on schooling fish. Omura's whales are rorquals, meaning they have long throat pleats that extend from the mouth to the naval; these skin flaps allow the whales mouth to expand so it can take in water, and sift through the krill and plankton within it, more efficiently.[3] Their distribution remains unknown, but they are known to occupy the coasts of Japan, the Philippines, Indonesia, and are thought to live in the subtropical waters of the Indian ocean and the western Pacific ocean. Since this whale was discovered so recently, and their discovery was based upon nine individuals, the IUCN has listed them as "data deficient", meaning there are no accurate approximations for their population.[4][16] Omura's whale
Pygmy right whale (Caperea marginata) status DD The pygmy right whale is a very elusive species; they are rarely seen in the ocean and much of what is known about them comes from dead individuals that stranded themselves onto shore, and, as a result, little is known about them. This whale was once thought to be the last surviving member of the Neobalaenidae family, but its skull shape suggests that it is part of a very ancient family of whales called cetotheres, which branched off from modern baleen whales somewhere between 17 million and 25 million years ago; the last member was thought to die out around two million years ago.[17] The name comes from its appearance, mainly the shape of the mouth.[18] Its length is 5.5 to 6.5 metres (18 to 21 ft) making it one of the smallest baleen whale species. Their average age remains unknown. It weighs 3 to 4 metric tons (3.3 to 4.4 short tons). The lower jaw is bowed and protrudes slightly. The body is stocky. They have a dark-coloured back, which becomes darker with age, and a pale belly. This whale has a prominent dorsal fin. The flippers are small and rounded and located under the body. The tail flukes are broad. The baleen plates are yellowish and are up to 70 centimetres (28 in) in length. It is only known from the Southern Hemisphere and usually is solitary. The stomach contents of beached whales identifies plankton and krill as a large part of their diet. Hunting behavior is not known, but, given their small lungs, they're thought they hunt near the surface.[4][5][6][19] Pygmy right whale
Right whale (Eubalaena glacialis, Eubalaena australis, Eubalaena japonica) These whales were named right whales, because for the early whalers they were the right ones to catch. They are slow, have lots of fat and stay afloat when killed. Only when the right and bowhead whales were depleted and factory ships were developed did the hunt for the rorquals start.[20] This 11 to 18 metres (36 to 59 ft) long species weighs 30 to 75 metric tons (33 to 83 short tons). Their average lifespan remains unknown, but some speculate they can live to be as old as 80. The right whale is extremely fat. There are numerous callosities on the mouth and head, caused by whale lice. They are black with large white patches on the belly. They have no dorsal fin and their flippers are paddle-shaped. The tail flukes are very wide, thin and pointed. Its distribution is in temperate oceans worldwide. The southern right whale (E. australis) can be found from the Antarctic to Australia and South America and into the Indian Ocean. The Northern right whale (E. japonica) is found in the North Pacific, from Japan and Baja California to the Aleutians. In the North Atlantic, the Northern atlantic right whale (E. glacialis) occurs from Florida and Spain in the South to Bear Island and Spitsbergen in the north. Its social structure is usually small groups of up to 5. They feeds mainly on krill and copepods. Right whales are balaenids, meaning they use their 500 massive baleen plates to take in water; balaenids lack throat pleets, but their head makes up around 40% of their body mass.[8] In the Northwest Atlantic about 1,000 are left; the Northeast Atlantic population is believed to be near extinction. The North Pacific population is probably nearly extinct. There are no signs of recovery in the Northern right whale populations. The total population of southern right whales is probably about 1,500 and may be recovering slightly.[4][5][6] Southern right whale
Sei whale (Balaenoptera borealis) status EN The sei whale is probably the fastest swimmer among the baleen whales. It can reach speeds of close to 38 km/hr. The sei whale has been hunted extensively in the past. Because this whale resembles the Bryde's whale (only at close range can one see the single ridge on the head, whereas the Bryde's whale has 3 parallel ridges), combined quotas were set for these species until 1964. The catches were also recorded together. Consequently, there is no accurate catch statistics from before that date. In the 1960s, the annual catch of Sei whales was 10-15,000 per year. Hunting of sei whales was stopped in the 1970s.[21] Typical males are 12 to 18 metres (39 to 59 ft) long, while females are up to 20 metres (66 ft) long. Males weigh up to 22 metric tons (24 short tons), females up to 24 metric tons (26 short tons). Their average age is 50 to 70 years. The sei whale is dark grey on the back and also on the underside of the tail stock. The chin, throat and belly are white. This whale often has oval white marks, caused by lampreys and cookiecutter sharks. One long ridge runs from the tip of the upper jaw to the blowholes. The dorsal fin is large and placed far back (farther than that of the fin whale). It has a worldwide distribution, but not near the pack ice. It is usually seen alone or in pairs. When plenty of food is available they may form larger groups. Diet consists mostly of krill and other crustaceans. The sei whale also feeds on capelin, pollack (in Norwegian, they are called sei; the association with this fish gave the whale its name), anchovies, herring, cod and sardines. Sei whales are rorquals, meaning they have long throat pleats that extend from the mouth to the naval; these skin flaps allow the whales mouth to expand so it can take in water, and sift through the krill and plankton within it, more efficiently.[3] This species has been depleted by over-exploitation. After the end of commercial whaling for this species in 1980, no population estimates have been made. The North Atlantic population probably consists of a few thousand, the North Pacific population about 13,000 and the Antarctic populations about 40,000. This species is still vulnerable.[4][5] Sei whale

Toothed whales

There are 72 species of toothed whale, which encompasses everything belonging to the suborder Odonteceti. Excluding dolphins and porpoises, there are 26 (recognized) species of toothed whales. [22]

Species Description Image
Beaked whale (Subfamily Berardiinae, Hyperoodontinae, Ziphiinae) Beaked whales are a member of the Ziphiidae family which encompasses 22 different species of whales (Andrew's beaked whale, Arnoux's beaked whale, Baird's beaked whale, Blainville's beaked whale, bottlenose whale, Cuvier's beaked whale, Deraniyagala's beaked whale, Gervais' beaked whale, Ginkgo-toothed beaked whale, Gray's beaked whale, Hector's beaked whale, Hubbs' beaked whale, Longman's beaked whale, Perrin's beaked whale, Pygmy beaked whale, Shepherd's beaked whale, Sowerby's beaked whale, Spade-toothed whale, Stejneger's beaked whale, Strap-toothed whale, and True's beaked whale [23]), all of which dive regularly to a depth surpassing 500 m (1,600 ft) to literally suck the life of their prey by using a suction system aided by a pair of grooves on the under its head which allow greater amounts of water to be in its mouth at one time. The Ziphiidae family is the most widespread of the cetaceans, encompassing the globes ocean, but generally inhabiting offshore areas of at least a depth of 300 m (980 ft). The beaked whale ranges from 4–13 m (13–43 ft), and weighing 0.9 to 13.6 metric tons (0.99 to 14.99 short tons). These whales are not dissimilar to dolphins, in that they both have beaks, have a bulging forehead, and are roughly the same dimensions as one. They do, however, have differences, in that their tail fluke does not have a notch in it (with the exception of Shepherd's beaked whale). Species differentiation can be difficult, in that all species are quite similar, except minute differences in size, colour, and beak size.[4][24] Blainville's beaked whale
Beluga whale (Delphinapterus leucas)
status NT
The beluga is a white whale that inhabits the icy waters of the Arctic Ocean. To cope with the freezing temperatures of the Arctic, belugas have an enormous amount of blubber that makes up 40% of their body mass. Belugas are also unique among cetaceans in that their skin turns yellow in July when it's time to shed it. Belugas are opportunistic, in that they'll eat just about anything that can realistically fit in its mouth, which could include octopus, squid, crustaceans, shellfish, snails, sand worms, and fish. They mainly use two different hunting methods: they can herd fish or forage for shellfish near the bottom. Belugas give birth to one (rarely two) calves every two to three years, with gestation lasting around 15 months. They nurse for the first 18 months when their teeth grow in. Belugas are also known for their incredibly sized pods that can include several hundred individuals and are given their nickname "canary of the sea" due to their high inclination to vocalize. Historically, belugas have been hunted by natives, but in more recent times (18th and 19th centuries), belugas have been hunted, mainly for their melon oil which was used as a lubricant.[25] Males average about 1,500 kg (3,300 lb), whereas females average about 1,360 kg (3,000 lb). Males can reach lengths of 4.15 m (13.6 ft), whereas females reach about 3.55 m (11.6 ft). Their average lifespan is thought to range anywhere from 35 years to 50 years.[4][26] Beluga whale
Dwarf sperm whale (Kogia sima)
status DD
Originally considered the same species as the pygmy sperm whale, a Smithsonian scientist determined they were two different species in 1966. The dwarf sperm whale is a smaller relative of Physeter macrocephalus and is almost the same as its closer cousin Kogia breviceps. Likewise, they have a spermaceti organ. This is a very elusive animal and, consequently, little is known about them. They are the only whales, apart from the pygmy sperm whale to use a sort of pseudo-ink, like squids, by releasing up to 12 gallons of a reddish/brown liquid when startled which is known as "the squid-tactic". This blurs the vision of its attacker, allowing the whale to escape unharmed. This whale has a false gill plate behind the eyes. These creatures are thought to dive to about 300 m (980 ft), and probably use echolocation to find their prey which includes squid, fish and crustaceans in the subtropical waters of the world. They are often seen logging near the surface at three knots. Dwarf sperm whales grow to be around 2.7 m (8 ft 10 in) in length, and weigh in at 135 to 270 kg (298 to 595 lb), with the females being slightly smaller than the males. They are thought to swim in pods of between six and ten individuals. Their population lies between 23,000 and 30,000 individuals in U.S. waters.[4][27] Dwarf sperm whale
Narwhal (Monodon monoceros) status NT The narwhal is a torpedo shaped whale that inhabits the icy waters of the Arctic Ocean. Narwhals have two teeth in their upper jaw and, in males, the left tooth grows into a large spiral tusk made of ivory that can be 2.7 m (8 ft 10 in) long and weigh 10 kg (22 lb), giving it its nickname "the unicorn of the sea". Females, rarely however, can also grow tusks.[28] Native Inuit hunted them for their skin which is eaten raw with a layer of fat. In the 1980s, this practice increased, which drastically reduced the narwhal's population. Their diet consists primarily of Greenland halibut, Arctic cod, cuttlefish, shrimp and armhook squid. Narwhals are believed to swim in pods of up to 20 individuals, usually segregated by gender. Generally, gestation requires around 15 months, and the calf (rarely calves) is weaned off after 20 months. The average male measures 4.7 m (15 ft), whereas the average female measures 4 m (13 ft). The male narwhal, on average, weighs 1,600 kg (3,500 lb) and the average female weighs 900 kg (2,000 lb), of which one third is fat to insulate themselves from the icy waters of the Arctic Ocean. They're thought to live up to 50 years. The narwhal has a conservation status of Near Threatened with an estimated population anywhere between 25,000 individuals to 45,000 individuals.[4][29]
Pygmy sperm whale (Kogia breviceps)
status DD
Originally considered the same species as the dwarf sperm whale, a Smithsonian scientist determined they were two different species in 1966. The pygmy sperm whale is a smaller relative of Physeter macrocephalus and is almost the same as its closer cousin Kogia sima. Likewise, they have a spermaceti organ. This is a very elusive animal and, consequently, little is known about them. They are the only whales, apart from the dwarf sperm whale to use a sort of pseudo-ink, like squids, by releasing up to 12 gallons of a reddish/brown liquid when startled which is known as "the squid-tactic". This blurs the vision of its attacker, allowing the whale to escape unharmed. This whale has a false gill plate behind the eyes. These creatures dive to about 300 m (980 ft), and probably use echolocation to find their prey which includes squid, fish and crustaceans in the subtropical and temperate waters of the world. They are often seen logging near the surface at three knots. Pygmy sperm whales grow to be around 3.5 m (11 ft) in length, and weigh in at 320 to 455 kg (705 to 1,003 lb), with the females being slightly smaller than the males. They are thought to swim in pods of up to seven individuals. The average lifespan of this whale is thought to be around 23 years. Their population remains unknown.[4][30] Pygmy sperm whale depiction from the 19th century
Sperm whale (Physeter macrocephalus) status VU Sperm whales are known for their enormous heads, likewise their brains are the largest in the animal kingdom with a volume of 8,000 cubic centimetres (490 in3) and weighs in at 7 kg (15 lb). These colossal creatures must dive as deep as 1,000 m (3,300 ft) in search of squid which makes up its diet, and to do such, they must hold their breath for 90 minutes. They do this frequently, due to their need to eat about 907 kilograms (1.000 short ton) of fish and squid per day. Female sperm whales congregate in pods of 15-20 individuals and remain in tropical waters year-round, whereas males travel alone in Arctic or Antarctic waters, feeding on the abundant squid, only migrating towards the equator to breed. Throughout the 18th and 19th centuries, sperm whales were heavily whaled for spermaceti (hence the name sperm whale), an oil that forms above its skull, which would be used in lubrication and lamp fuel; this ended in 1985 when the International Whaling Commission created a treaty between whalers, that practically ended it. Sperm whale oil was, and is, a valuable commodity. Sperm whales weigh up to 40 metric tons (44 short tons), and can be as long as 18 m (59 ft). Typically, they live to be 70 years old. The sperm whale is endangered with a population is dwindling at 300,000 individuals.[4][31][32] Mother and baby sperm whales

Evolution All cetaceans, including whales, dolphins, and porpoises, are descendants of land-dwelling mammals of the artiodactyl order (even-toed ungulates). All cetaceans are related to the Indohyus, an extinct chevrotain-like ungulate, from which they split approximately 48 million years ago.[33][34]

These primitive cetaceans, or archaeocetes, first took to the sea approximately 49 million years ago and became fully aquatic by 5–10 million years later.[35] Their features became adapted for living in the marine environment. Major anatomical changes include streamlining of the body, the migration of the nasal openings toward the top of the cranium, the shrinking and eventual disappearance of the hind limbs, the modification of the forelimbs into flippers, and the growth of flukes on the tail.

Today, the closest living relative of cetaceans is the hippo. Whales and hippos share a semi-aquatic ancestor that branched off from other artiodactyls some 60 million years ago.[36][37] Around 40 million years ago, a common ancestor between the two branched off into cetacea and anthracotheres; anthracotheres went extinct at the end of the Pleistocene two-and-a-half million years ago, eventually leaving only one surviving lineage: the hippo.[38][39]

Archaeocetes

Evolution of whales
Indohyus (Archaeoceti cca 49–48 Ma)
Pakicetus (Archaeoceti cca 49–48 Ma)
Ambulocetus (Archaeoceti cca 49–48 Ma)
Kutchicetus (Archaeoceti cca 48 Ma)
Rodhocetus (Archaeoceti cca 45 Ma)
Protocetus (Archaeoceti cca 45 Ma)
Dorudon (Archaeoceti cca 35 Ma)
Squalodon (Odontoceti cca 25 Ma)
Kentriodon (Odontoceti cca 20 Ma)
Janjucetus (Mysticeti cca 25 Ma)
Cetotherium (Mysticeti cca 18 Ma)

Archaeoceti is a suborder comprising ancient whales. These ancient whales are the predecessors of modern whales, stretching back to their first ancestor that spent their lives near (rarely in) the water. Likewise, the archaeocetes can be anywhere from near fully terrestrial, though these are found on the Indian subcontinent, to semi-aquatic to fully aquatic, but what defines an archaeocete is the presence of features not present in modern whales; this would include visible legs or asymmetrical teeth.[4][40][41][42][43]

Indohyus was a small chevrotain-like animal that lived about 48 million years ago in what is now the Kashmir.[44] It belongs to the family Raoellidae, and is believed to be the closest sister group of cetacea.[45] This herbivorous creature shared some whale-like traits, most notably the involucrum, a bone growth pattern found exclusively in cetaceans.[46] It also showed signs of adaptations to aquatic life, including a thick and heavy outer coating and dense limb bones that act as ballasts, which are similar to the adaptions found in modern creatures such as the hippopotamus; this suggests that, when in danger, it dived into the water and stayed in there for many minutes.[47][48][49][50][40][51][52]

Pakicetus was a terrestrial hoofed mammal that is thought to be the one of the earliest known whales, with Indohyus being the closest sister group.[53] It belonged to the Pakicetidae family. They lived around 50 million years ago. Their fossils were first discovered in North Pakistan in 1979, in what was the Tethys sea. After the initial discovery, more fossils were found, all in the fluvial deposits in northern Pakistan and northwestern India. Based on this discovery, pakicetids most likely lived in an arid environment with ephemeral streams and moderately developed floodplains millions of years ago. Their skeleton implies a running lifestyle, but stable oxygen isotopes analysis shows that they lived near freshwater (and probably foraged in freshwater). Their diet probably included land animals that approached water (who would get ambushed and drown) or some freshwater aquatic organisms that lived in the river.[40][49][50][51]

Ambulocetus natans, which lived about 49 million years ago, was discovered in Pakistan in 1994 and belonged to the Ambulocetidae family. It was probably amphibious, and resembled the crocodile in its physical appearance; likewise, it was probably no longer herbivorous.[54] In the Eocene, ambulocetids inhabited the estuaries of the Tethys sea in northern Pakistan.[45] The fossils of ambulocetids are always found in near-shore shallow marine deposits associated with abundant marine plant fossils.[55] Although they are found only in marine deposits, their oxygen isotope values indicate that they drank a range of water with different degree of salinity, with some specimens having no evidence of sea water consumption and others that did not ingest fresh water at the time when their teeth are fossilized. It is clear that ambulocetids tolerated a wide range of salt concentrations and, therefore, represent a transitional phase of whale ancestors between fresh water and the ocean. In addition to this, they used a new hearing method allowing them to better hear underwater; sound traveled through soft tissue in the jaw leading to the ear. Modern whales use this system today.[40][49][50][51][56]

Kutchicetus evolved about 45 million years ago, belonged to the Remingtonocetidae family and was first described in 1986. It was probably amphibious, more so than its ancestors, of course. It had a much more flattened vertebrae than Ambulocetus natans, which would've supported an otter-like tail; the hip and vertebrae were still fused together, meaning they still walked on land. Its fossils were found in sediment that formed in shallow seas protected by barrier islands, meaning it had ventured into the oceans. Their eyes, much like Ambulocetus natans, were at high up on the skull, meaning they had a crocodile-like posture. The presence of foramina near the tip indicates they had whiskers. Their skull also had a very large sagittal crest, meaning they had a lot of room for jaw muscles; nobody knows exactly why they had this.[40][49][50]

Protocetus evolved around 43 million years ago, and belonged to the Protocetidae family and was first described in 1908. It was more suited for a marine environment in comparison to its ancestors, but, nonetheless, still was amphibious. They had their pelvis only loosely connected to their sacral vertebrae, which allowed for greater movement in water, but it made them clumsy on land. It is thought they walked much like seals. They also had their nostrils further up their snout; this would eventually be at the top of their head. A fossil of Maiacetus, another protocetid, showed the fetus positioned for head-first delivery, indicating they gave birth on land; if they did give birth in the seas, the baby would be positioned tail-first to reduce risk of drowning.[57] Protocetids were the first archaeocetes to leave India.[40][50]

Basilosaurus, which lived about 35 million years ago, belonged to the Basilosauridae family, and are sometimes referred to as zeuglodons. They were discovered in 1868 in marine deposits, and their bones are found in Pakistan, the Middle East, and North America. Their pelvis was completely detached from their vertebrae, meaning they could no longer support themselves on land; they did, however, have very small feet containing three digits that, possibly, was used during courtship. Their nostrils were positioned at the top of their head, and the earbone structure indicates that it could hear very well in its marine environment. Their forelimbs were flippers, and their vertebrae suggests they had tail flukes. Their stomach contents indicated that they ate fish.[40][49][50]

Dorudon, which lived 35 million years ago, belonged to the Basilosauridae family. They were discovered in 1923 in marine deposits, and their bones are found worldwide. Their pelvis was completely detached from their vertebrae and their hind limbs were tiny, meaning they could no longer support themselves on land. Its nostrils were now at the top of its head, and they could, like modern whales, hear very well underwater. Their forelimbs were flippers. Their stomach contents indicated that they ate fish. They are suspected to have been preyed upon by Basilosaurus, given their major injuries sustained during their lifetime.[50][58]

Toothed or Baleen Odontocetes (toothed whales) and mysticetes (baleen whales) split into two separate suborders around 34 million years ago.[59][60][61]

The adaptation of echolocation defines when toothed whales split apart from baleen whales, and distinguishes modern toothed whales from ancient toothed whales. Modern toothed whales do not rely on their sense of sight, but rather on their sonar to hunt prey. Echolocation also allowed toothed whales to dive deeper in search of food, with light no longer necessary for navigation, which opened up new food sources.[62] Toothed whales (Odontocetes) echolocate by creating a series of clicks emitted at various frequencies. Sound pulses are emitted through their melon-shaped foreheads, reflected off objects, and retrieved through the lower jaw. Skulls of Squalodon show evidence for the first hypothesized appearance of echolocation.[citation needed] Squalodon lived from the early to middle Oligocene to the middle Miocene, around 33-14 million years ago. Squalodon featured several commonalities with modern Odontocetes. The cranium was well compressed, the rostrum telescoped outward (a characteristic of the modern suborder Odontoceti), giving Squalodon an appearance similar to that of modern toothed whales. However, it is thought unlikely that squalodontids are direct ancestors of living dolphins.[40][49]

The earliest known ancestor of modern monodontids is Denebola brachycephala from the late Miocene around 9–10 million years ago.[63] A single fossil from Baja California indicates the family once inhabited warmer waters.[64] The fossil record also indicates D. brachycephala's range varied with that of the polar ice packs expanding during ice ages and contracting when the ice retreated.[40][65]

Ancient sperm whales differ from modern sperm whales in tooth count and the shape of the face and jaws. For example, Scaldicetus had a tapered rostrum. Genera from the Oligocene and Miocene, with the exception of Aulophyseter, had teeth in their upper jaws. Acrophyseter also had teeth in both the upper and lower jaws as well as a short rostrum and an upward curving mandible. These anatomical differences suggest that these ancient species may not have necessarily been deep-sea squid hunters like the modern sperm whale, but that some genera mainly ate fish.[40][66] Contrary to modern sperm whales, ancient sperm whales were built to hunt whales. Livyatan melvillei, residing along ancient Peru 12 million years ago, had a short and wide rostrum measuring 3 metres (9.8 ft) across. This gave the whale the ability to inflict major damage on large struggling prey. This mouth was specially adapted for eating eobalaenids, and did so much more effectively than other, more famous, predators such as Megalodon. Other physeteroids such as Zygophyseter and Brygmophyseter, collectively known as killer sperm whales, also preyed upon early baleen whales, as well as seals.[66][67]

Beaked whales consist of over 20 genera.[68][69] Some included ancestors of giant beaked whales, Berardius, such as Microberardius, and Cuvier's beaked whale, Ziphius, had many relatives, such as Caviziphius, Archaeoziphius, and Izikoziphius. They were probably preyed upon by killer sperm whales and sharks such as Megalodon as many other species were. Recently, a large fossil Ziphiid sample was discovered off the coast of South Africa, confirming the remaining ziphiid species might just be a remnant of a higher diversity that has since gone extinct. After studying numerous fossil skulls, researchers discovered the absence of functional maxillary teeth in all South African ziphiids, which is evidence that suction feeding had already developed in several beaked whale lineages during the Miocene. Researchers also found extinct ziphiids with robust skulls, signaling that tusks were used for male-male interactions (speculated with extant beaked whales).[68]

The earliest of baleen whales contained both teeth and baleen in their jaws, as with Llanocetus, but Aetiocetus is considered to be the earliest.[70] The earliest whale with only baleen was found in New Zealand, and it was 26 million years old. Baleen plates are used to seethe the water in search of plankton and krill, allowing for a greater variety of food available than toothed whales. These microscopic organisms reside near the surface of the water, and baleen whales are forced to follow their migratory patterns; Most species reside at the poles, however, where they feed on a reliable source of plankton and krill. These arctic, and antarctic, whales have to go to warmer waters to give birth or risk their young dying of frostbite.[40]

The main reason whales migrated to the poles, however, is due to the lack of predators that far north or south. Eobalaenids were relatively small compared to modern mysticetes, roughly 10 metres (33 ft), and were preyed upon by the large mega-fauna of the Pleistocene. While residing in the tropics, eobalaenids were frequently preyed upon by killer sperm whales or large sharks, such as Megalodon. To seek refuge, these early whales migrated to the poles where neither dare to follow, and they also found an abundance of krill and plankton.[40][49]

Eobalaenids were relatively small compared to their descendants due to their difference in diet which, for them, was mainly schooling fish. As their usage of baleen progressively grew, so did they. This is due to a simple matter of energy found in the trophic levels. This basically states that the higher up a creature is on the food chain, the less energy it consumes. Modern baleen whales consume mainly phytoplankton, zooplankton, and krill which are the foundation of the photic zone's ecosystem. Since they are primary consumers, and they eat tons of them per day, there is a correlation between baleen dependency and size.[40][71][72]

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