Editing Cetacea (section)

{{Short description|Infraorder of mammals}}
{{Automatic taxobox
| fossil_range      = {{geological range|53.5|0|earliest=|latest=|PS=}}Early [[Eocene]] – Present
| image = {{Multiple image
| perrow            = 2/2/2
| total_width       = 275
| caption_align = center
| image1            =  Mother and baby sperm whale.jpg
| caption1          = [[Sperm whale]]
| image2            = Humpback stellwagen edit.jpg
| caption2          = [[Humpback whale]]
| image3            = Killerwhales jumping.jpg
| caption3          = [[Orca]]
| image4            = Eubalaena glacialis with calf.jpg
| caption4          = [[North Atlantic right whale]]
| image5            = Amazonas-Flussdelfin Orinoko3.jpg
| caption5          = [[Amazon river dolphin]] 
| image6            = Marsvin (Phocoena phocoena) light.jpg
| caption6          = [[Harbor porpoise]]
| border            = infobox
}}
| taxon             = Cetacea
| authority         = [[Mathurin Jacques Brisson|Brisson]], 1762
| subdivision_ranks = Subgroups
| subdivision       =
*†[[Pakicetidae]]
*†[[Ambulocetidae]]
*†[[Remingtonocetidae]]
*†[[Protocetidae]] ([[paraphyletic]])
*'''Pelagiceti''' <small>Uhen, 2008</small><ref>{{cite journal |author=Uhen, M.D. |year=2008 |title=New protocetid whales from Alabama and Mississippi, and a new Cetacean clade, Pelagiceti |journal=[[Journal of Vertebrate Paleontology]] |volume=28 |issue=3 |pages=589–593 |doi=10.1671/0272-4634(2008)28[589:NPWFAA]2.0.CO;2 |jstor=20490986 |s2cid=86326007}}</ref>
**†[[Basilosauridae]] (paraphyletic)
**†[[Kekenodontidae]]
**'''Neoceti''' <small>Fordyce & de Muizon, 2001</small><ref>{{cite conference |author1=Fordyce, E. |author2=de Muizon, C. |year=2001 |title=Evolutionary history of the cetaceans: a review |editor1=Mazin, J.-M. |editor2=de Buffrénil, V. |book-title=Secondary Adaptations of Tetrapods to Life in the Water: Proceedings of the international meeting, Poitiers, 1996 |publisher=[[:de:Verlag Dr. Friedrich Pfeil|Verlag Dr. Friedrich Pfeil]] |place=München, Germany |pages=169–233 |isbn=3-931516-88-1 |lccn=2002550356 |oclc=52121251 |ol=20591860M}}</ref>
***[[Mysticeti]]
***[[Odontoceti]]
''([[#Classification|see text]] for families)''
| diversity        = Around 94 species
| diversity_link   = List of cetaceans
}}

'''Cetacea''' ({{IPAc-en|s|ɪ|ˈ|t|eɪ|ʃ|ə}}; {{etymology|la|cetus|[[whale]]}}, {{etymology|grc|''κῆτος'' ({{grc-transl|[[Cetus (mythology)|κῆτος]]}})|[[list of largest fish|huge fish]], [[sea monster]]}})<ref>{{cite journal |url=http://aquaticmammalsjournal.org/share/AquaticMammalsIssueArchives/2001/AquaticMammals_27-02/27-02_Ranneft.PDF |archive-url=https://web.archive.org/web/20160327235028/http://www.aquaticmammalsjournal.org/share/AquaticMammalsIssueArchives/2001/AquaticMammals_27-02/27-02_Ranneft.PDF |archive-date=2016-03-27 |url-status=live |first1=D.|last1=M. Raneft |first2=H.|last2=Eaker |first3=R.|last3=W. Davis |year=2001 |title=A guide to the pronunciation and meaning of cetacean taxonomic names |journal=Aquatic Mammals |volume=27 |issue=2 |page=185}}</ref> is an [[infraorder]] of [[aquatic mammal]]s belonging to the order [[Artiodactyla]] that includes [[whale]]s, [[dolphin]]s and [[porpoises]]. Key characteristics are their fully aquatic lifestyle, [[streamlined]] body shape, often large size and exclusively [[carnivorous]] diet. They propel themselves through the water with powerful up-and-down movement of their tail, which ends in a paddle-like fluke, using their flipper-shaped forelimbs to maneuver.<ref>{{cite journal|last=E. Fish|first=Frank|year=2002|title=Balancing Requirements for Stability and Maneuverability in Cetaceans|journal=Integrative and Comparative Biology|volume=42|issue=1|pages=85–93|doi=10.1093/icb/42.1.85|pmid=21708697|s2cid=25036870|doi-access=free}}</ref>

While the majority of cetaceans live in marine environments, a small number reside solely in [[brackish water]] or [[fresh water]]. Having a [[cosmopolitan distribution]], they can be found in some rivers and all of Earth's oceans, and many species inhabit vast ranges where they migrate with the changing of the seasons.

Cetaceans are famous for [[cetacean intelligence|their high intelligence]], complex social behaviour, and the enormous size of some of the group's members. For example, the [[blue whale]] reaches a maximum confirmed length of {{convert|29.9|m|ft|abbr=off|sp=us}} and a weight of 173 tonnes (190 short tons), making it the largest animal ever known to have existed.<ref name="Wood">Wood, Gerald ''The Guinness Book of Animal Facts and Feats'' (1983) {{ISBN|978-0-85112-235-9}}</ref><ref>{{cite web|last1=Davies|first1=Ella|date=2016-04-20|title=The longest animal alive may be one you never thought of|url=http://www.bbc.com/earth/story/20160420-the-longest-animal-alive-may-not-be-the-blue-whale|access-date=2018-02-14|website=BBC Earth|language=en}}</ref><ref>{{cite web|title=Largest mammal|url=http://www.guinnessworldrecords.com/world-records/largest-mammal|website=Guinness World Records}}</ref>

There are approximately 89<ref>{{Cite web|last=Perrin|first=W.F.|date=2020|title=World Cetacea Database|url=http://www.marinespecies.org/cetacea|access-date=2020-12-12|website=marinespecies.org}}</ref> living species split into two [[parvorder]]s: [[Odontoceti]] or toothed whales (containing [[porpoise]]s, [[dolphin]]s, other predatory whales like the  [[beluga whale|beluga]] and the [[sperm whale]], and the poorly understood [[beaked whale]]s) and the filter feeding [[Mysticeti]] or [[baleen]] whales (which includes species like the [[blue whale]], the [[humpback whale]] and the [[bowhead whale]]). Despite their highly modified bodies and carnivorous lifestyle, genetic and fossil evidence places cetaceans as nested within [[even-toed ungulate]]s, most closely related to [[Hippopotamidae|hippopotamus]] within the clade [[Whippomorpha]].

Cetaceans have been extensively [[whaling|hunted]] for their meat, [[blubber]] and [[Whale oil|oil]] by commercial operations. Although the [[International Whaling Commission]] has agreed on putting a halt to commercial whaling, whale hunting is still going on, either under IWC quotas to assist the subsistence of Arctic native people or in the name of scientific research, although a large spectrum of non-lethal methods are now available to study marine mammals in the wild.<ref>{{cite journal |last1=Notarbartolo di Sciara |first1=G. |last2=Briand |first2=F. |date=2004 |title=Investigating the Roles of Cetaceans in Marine Ecosystems - An overview |journal=CIESM Workshop Monographs |volume=25 |pages=1–15}}[https://www.researchgate.net/publication/289532221]</ref> Cetaceans also face severe environmental hazards from underwater [[Noise pollution#Wildlife|noise pollution]], entanglement in abandoned ropes and nets, collisions with ships, plastic and heavy metals build-up, to accelerating [[climate change]],<ref name="wdcs2">{{cite book|author=Cara E. Miller|url=http://uk.whales.org/sites/default/files/whales-and-dolphins-in-the-pacific-islands.pdf|title=Current State of Knowledge of Cetacean Threats, Diversity, and Habitats in the Pacific Islands Region|publisher=Whale and Dolphin Conservation Society|year=2007|isbn=978-0-646-47224-9|access-date=5 September 2015|archive-url=https://web.archive.org/web/20150908003502/http://uk.whales.org/sites/default/files/whales-and-dolphins-in-the-pacific-islands.pdf|archive-date=8 September 2015|url-status=dead}}</ref><ref name="Nowacek2">{{cite journal|last1=Nowacek|first1=Douglas|last2=Donovan|first2=Greg|last3=Gailey|first3=Glenn|last4=Racca|first4=Roberto|last5=Reeves|first5=Randall|last6=Vedenev|first6=Alexander|last7=Weller|first7=David|last8=Southall|first8=Brandon|date=2013|title=Responsible Practices for Minimizing and Monitoring Environmental Impacts of Marine Seismic Surveys with an Emphasis on Marine Mammal|journal=Aquatic Mammals|volume=39|issue=4|pages=356–377|doi=10.1578/am.39.4.2013.356|bibcode=2013AqMam..39..356N }}<!--|access-date=April 2, 2016--></ref> but how much they are affected varies widely from species to species, from minimally in the case of the [[southern bottlenose whale]] to the [[baiji]] (Chinese river dolphin) which is considered to be functionally extinct due to human activity.<ref name="baiji">{{cite news|last=Lovgren|first=Stefan|date=December 14, 2006|title=China's Rare River Dolphin Now Extinct, Experts Announce|work=National Geographic News|publisher=[[National Geographic Society]]|location=Washington, D.C.|url=http://news.nationalgeographic.com/news/2006/12/061214-dolphin-extinct.html|archive-url=https://web.archive.org/web/20061218185108/http://news.nationalgeographic.com/news/2006/12/061214-dolphin-extinct.html|url-status=dead|archive-date=December 18, 2006|access-date=2015-10-18}}</ref>