Editing Cetacea (section)

== Anatomy ==
[[File:Dolphin Anatomy.svg|thumb|upright=1.5|Dolphin anatomy]]

Cetacean bodies are generally similar to those of fish, which can be attributed to their lifestyle and the habitat conditions. Their body is well-adapted to their habitat, although they share essential characteristics with other higher mammals ([[Eutheria]]).<ref name="autogenerated2">{{cite news |last1=Groves |last2=Colin |first3=Peter |last3=Grubb |title=Ungulate taxonomy |newspaper=JHU Press |year=2011}} {{page needed|date=April 2018}}</ref>

They have a streamlined shape, and their forelimbs are [[Flipper (anatomy)|flippers]]. Almost all have a [[dorsal fin]] on their backs, but this can take on many forms, depending on the species. A few species, such as the [[beluga whale]], lack them. Both the flipper and the fin are for stabilization and steering in the water.{{citation needed|date=October 2024}}

The male genitals and the mammary glands of females are sunken into the body.<ref name="Thewissen2013">{{cite book |author=[[Hans Thewissen|Thewissen]], J.G.M.  |title=The Emergence of Whales: Evolutionary Patterns in the Origin of Cetacea |url=https://books.google.com/books?id=8QPyBwAAQBAJ&q=(penis+OR+genital)&pg=PA383 |date=11 November 2013 |publisher=Springer  |isbn=978-1-4899-0159-0 |pages=383–}}</ref><ref name="Miller2007">{{cite book |author=Miller, Debra Lee |title=Reproductive Biology and Phylogeny of Cetacea: Whales, Porpoises and Dolphins |url=https://books.google.com/books?id=sD3NBQAAQBAJ |date=2007 |publisher=CRC Press |isbn=978-1-4398-4257-7}}</ref> The male genitals are attached to a vestigial [[pelvis]].<ref>{{Cite book |last=Tinker |first=Spencer Wilkie |url=https://books.google.com/books?id=ASIVAAAAIAAJ&pg=PA93 |title=Whales of the World |date=1988-01-01 |publisher=Brill Archive |isbn=978-0-935848-47-2 |language=en}}</ref>

The body is wrapped in a thick layer of fat, known as [[blubber]]. This provides [[thermal insulation]] and gives cetaceans their smooth, streamlined body shape. In larger species, it can reach a thickness up to {{convert|1/2|m|ft|abbr=off|sp=us|spell=in}}.{{citation needed|date=October 2024}}

[[Sexual dimorphism]] evolved in many toothed whales. Sperm whales, [[narwhal]]s, many members of the [[beaked whale]] family, several species of the [[porpoise]] family, orcas, [[pilot whale]]s, eastern [[spinner dolphin]]s and [[northern right whale dolphin]]s show this characteristic.<ref name="ReferenceA">{{cite journal |last1=Dines |first1=James |last2=Mesnick |first2=Sarah |last3=Ralls |first3=Katherine |last4=May-Collado |first4=Laura |last5=Agnarsson |first5=Ingi |last6=Dean |first6=Matthew |title=A trade-off between precopulatory and postcopulatory trait investment in male cetaceans |journal=Evolution |date=2015 |volume=69 |issue=6 |pages=1560–1572 |doi=10.1111/evo.12676 |pmid=25929734|s2cid=18292677 }}</ref> Males in these species developed external features absent in females that are advantageous in combat or display. For example, male sperm whales are up to 63% percent larger than females, and many beaked whales possess tusks used in competition among males.<ref name="ReferenceA" /><ref>{{cite journal |last1=Dalebout |first1=Merel |last2=Steel |first2=Debbie |last3=Baker |first3=Scott |title=Phylogeny of the Beaked Whale Genus ''Mesoplodon'' (Ziphiidae: Cetacea) Revealed by Nuclear Introns: Implications for the Evolution of Male Tusks|journal=Systematic Biology |date=2008 |volume=57 |issue=6 |pages=857–875 |doi=10.1080/10635150802559257 |pmid=19085329|s2cid=205729032 |doi-access=free }}</ref>
Hind legs are not present in cetaceans, nor are any other external body attachments such as a [[pinna (anatomy)|pinna]] and [[hair]].<ref>{{Cite web|url=http://www.eurekalert.org/pub_releases/2006-05/uof-haw052206.php|title=How ancient whales lost their legs, got sleek and conquered the oceans|date=2006-05-22|website=EurekAlert|publisher=University of Florida|access-date=2016-03-20|archive-date=2020-12-02|archive-url=https://web.archive.org/web/20201202154340/https://www.eurekalert.org/pub_releases/2006-05/uof-haw052206.php|url-status=dead}}</ref>

=== Head ===
{{multiple image
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|image1=Beluga premier.gov.ru-1.jpeg
|caption1=Head profile of a [[beluga whale]], featuring the large "melon" region

|image2=SBNMS - feeding humpback whale (31319806616).jpg
|caption2=Close up of a feeding [[humpback whale]], showing baleen

}}
Whales have an elongated head, especially [[baleen whales]], due to the wide overhanging jaw. Bowhead whale plates can be {{convert|9|m|ft}} long. Their nostril(s) make up the [[Blowhole (anatomy)|blowhole]], with one in toothed whales and two in baleen whales.<ref>{{Cite journal|last1=Buono|first1=Mónica R.|last2=Fernández|first2=Marta S.|last3=Fordyce|first3=R. Ewan|last4=Reidenberg|first4=Joy S.|date=2015|title=Anatomy of nasal complex in the southern right whale, Eubalaena australis (Cetacea, Mysticeti)|journal=Journal of Anatomy|language=en|volume=226|issue=1|pages=81–92|doi=10.1111/joa.12250|issn=1469-7580|pmc=4313901|pmid=25440939}}</ref>

The nostrils are located on top of the head above the eyes so that the rest of the body can remain submerged while surfacing for air. 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.<ref name="Klima1999">{{cite book|author=Milan Klima |title=Development of the Cetacean Nasal Skull|url=https://books.google.com/books?id=kOHAz9SCL54C |date=29 January 1999 |publisher=Springer |isbn=978-3-540-64996-0 }} {{page needed|date=April 2018}}</ref> 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.{{citation needed|date=October 2024}}

In toothed whales, connective tissue exists in the [[melon (cetacean)|melon]] as a head buckle. This is filled with air sacs and fat that aid in buoyancy and [[biosonar]]. The sperm whale has a particularly pronounced melon; this is called the [[spermaceti organ]] and contains the eponymous [[spermaceti]], hence the name "sperm whale". Even the long tusk of the narwhal is a vice-formed tooth. In many toothed whales, the depression in their skull is due to the formation of a large melon and multiple, asymmetric air bags.<ref>{{Cite journal |last1=Cranford |first1=Ted W. |last2=Amundin |first2=Mats |last3=Norris |first3=Kenneth S. |date=1996 |title=Functional morphology and homology in the odontocete nasal complex: Implications for sound generation |url=https://onlinelibrary.wiley.com/doi/10.1002/(SICI)1097-4687(199606)228:3%3C223::AID-JMOR1%3E3.0.CO;2-3 |journal=Journal of Morphology |language=en |volume=228 |issue=3 |pages=223–285 |doi=10.1002/(SICI)1097-4687(199606)228:3<223::AID-JMOR1>3.0.CO;2-3 |pmid=8622183 |issn=1097-4687}}</ref>

[[River dolphin]]s, unlike most other cetaceans, can turn their head 90°. Most other cetaceans have fused neck vertebrae and are unable to turn their head at all.{{citation needed|date=October 2024}}

The [[baleen]] of baleen whales consists of long, fibrous strands of keratin. Located in place of the teeth, it has the appearance of a huge fringe and is used to sieve the water for [[plankton]] and krill.<ref>{{Cite web |title=What is baleen? |url=https://us.whales.org/whales-dolphins/what-is-baleen/ |access-date=2025-01-13 |website=Whale & Dolphin Conservation USA |language=en-US}}</ref>

=== Brain ===
[[File:Preserved sperm whale brain.jpg|right|thumb|Brain of the [[sperm whale]], considered the largest brain in the world]]
Sperm whales have the largest brain mass of any animal on Earth, averaging {{convert|8,000|cm3|in3|abbr=on}} and {{convert|7.8|kg|lb|abbr=on}} in mature males.<ref>{{cite web | url=http://www.nmfs.noaa.gov/pr/species/mammals/cetaceans/spermwhale.htm |title=Sperm Whales brain size| publisher=NOAA Fisheries – Office of Protected Resources |access-date=9 August 2015}}</ref> The [[brain to body mass ratio]] in some odontocetes, such as belugas and narwhals, is second only to humans.<ref>{{cite magazine |url=http://blogs.scientificamerican.com/news-blog/are-whales-smarter-than-we-are/ |author=Fields, R. Douglas |title=Are whales smarter than we are? | magazine=Scientific American |access-date=9 August 2015}}</ref> In some whales, however, it is less than half that of humans: 0.9% versus 2.1%.{{citation needed|date=October 2024}}

In cetaceans, evolution in the water has caused changes to the head that have modified brain shape such that the brain folds around the insula and expands more laterally than in terrestrial mammals. As a result, the cetacean prefrontal cortex (compared to that in humans) rather than frontal is laterally positioned.<ref name="Gerussi Graïc Peruffo Behroozi 2023 pp. 1963–1976">{{cite journal |last1=Gerussi |first1=Tommaso |last2=Graïc |first2=Jean-Marie |last3=Peruffo |first3=Antonella |last4=Behroozi |first4=Mehdi |last5=Schlaffke |first5=Lara |last6=Huggenberger |first6=Stefan |last7=Güntürkün |first7=Onur |last8=Cozzi |first8=Bruno |date=2023 |title=The prefrontal cortex of the bottlenose dolphin (Tursiops truncatus Montagu, 1821): a tractography study and comparison with the human |journal=Brain Structure and Function |volume=228 |issue=8 |pages=1963–1976 |doi=10.1007/s00429-023-02699-8 |issn=1863-2661 |pmc=10517040 |pmid=37660322}}</ref>

[[Brain size]] was previously considered a major indicator of [[intelligence]]. Since most of the brain is used for maintaining bodily functions, greater ratios of brain to body mass may increase the amount of brain mass available for cognitive tasks. [[Allometric]] analysis of the relationship between mammalian brain mass (weight) and body mass for different species of mammals shows that larger species generally have larger brains. However, this increase is not fully proportional. Typically the brain mass only increases in proportion to somewhere between the two-thirds power (or the square of the cube root) and the three-quarters power (or the cube of the fourth root) of the body mass.
<big>''m''<sub>''brain''</sub> ∝ (''m''<sub>''body''</sub>)<sup>''k''</sup></big>
where ''k'' is between two-thirds and three-quarters. Thus if Species B is twice the size of Species A, its brain size will typically be somewhere between 60% and 70% higher.<ref>{{cite web |url=http://pages.ucsd.edu/~jmoore/courses/allometry/allometry.html |title=Allometry |first=Jim |last=Moore| publisher=University of California San Diego |access-date=9 August 2015}}</ref> Comparison of a particular animal's brain size with the expected brain size based on such an analysis provides an [[encephalization quotient]] that can be used as an indication of animal intelligence.<ref>{{cite book|last1=Pontarotti|first1=Pierre|title=Evolutionary Biology: Convergent Evolution, Evolution of Complex Traits|date=2016|publisher=Springer|isbn=978-3-319-41324-2|pages=74}}</ref>

The [[neocortex]] of many cetaceans is home to elongated [[spindle neurons]] that, prior to 2019, were known only in [[Hominidae|hominids]].<ref>{{cite journal |author=Watson, K.K. |title=Dendritic architecture of the Von Economo neurons |journal=Neuroscience |volume=141 |issue=3 |pages=1107–1112 |year=2006 |doi=10.1016/j.neuroscience.2006.04.084 |last2=Jones |first2=T. K. |last3=Allman |first3=J. M. |pmid=16797136|s2cid=7745280 }}<!--|access-date=29 August 2015--></ref> In humans, these cells are thought to be involved in social conduct, emotions, judgment and theory of mind.<ref>{{cite journal |author=Allman, John M. |title=Intuition and autism: a possible role for Von Economo neurons |journal=Trends Cogn Sci |volume=9 |issue=8 |pages=367–373 |year=2005 |doi=10.1016/j.tics.2005.06.008 |last2=Watson |first2=Karli K. |last3=Tetreault |first3=Nicole A. |last4=Hakeem |first4=Atiya Y. |pmid=16002323|s2cid=14850316 }}</ref> Cetacean [[spindle neuron]]s are found in areas of the brain homologous to where they are found in humans, suggesting they perform a similar function.<ref>{{cite journal |author=Hof, Patrick R. |title=Structure of the cerebral cortex of the humpback whale, ''Megaptera novaeangliae'' (Cetacea, Mysticeti, Balaenopteridae) |journal=The Anatomical Record |volume=290 |issue=1 |pages=1–31 |year=2007 |doi=10.1002/ar.20407 |last2=Van Der Gucht |first2=Estel |pmid=17441195|s2cid=15460266 |doi-access=free }}<!--|access-date=29 August 2015--></ref>

=== Skeleton ===
{{unreferenced section|date=April 2018}}
[[File:Whales skeletal system comparison.png|370px|thumb|Diagram featuring the typical skeletal of a toothed whale (top) and a baleen whale (bottom)]]
The cetacean skeleton is largely made up of [[cortical bone]], which stabilizes the animal in the water. For this reason, the usual terrestrial compact bones, which are finely woven [[cancellous bone]], are replaced with lighter and more elastic material. In many places, bone elements are replaced by cartilage and even fat, thereby improving their [[hydrostatic]] qualities. The ear and the muzzle contain a bone shape that is exclusive to cetaceans with a high density, resembling [[porcelain]]. This conducts sound better than other bones, thus aiding [[biosonar]].

The number of [[vertebrae]] that make up the spine varies by species, ranging from forty to ninety-three. The [[cervical spine]], found in all mammals, consists of seven vertebrae which, however, are reduced or fused. This fusion provides stability during swimming at the expense of mobility. The fins are carried by the [[thoracic vertebrae]], ranging from nine to seventeen individual vertebrae. The [[sternum]] is cartilaginous. The last two to three pairs of ribs are not connected and hang freely in the body wall. The stable lumbar and tail include the other vertebrae. Below the [[caudal vertebrae]] is the [[chevron (anatomy)|chevron bone]].

The front limbs are paddle-shaped with shortened arms and elongated finger bones, to support movement. They are connected by cartilage. The second and third fingers display a proliferation of the finger members, a so-called hyperphalangy. The shoulder joint is the only functional joint in all cetaceans except for the [[Amazon river dolphin]]. The [[collarbone]] is completely absent.

=== Fluke ===
<!--[[Fluke (tail)]] redirects directly here.-->
[[File:Humpback whale fluke (2).jpg|thumb|upright=1.2|Humpback whale fluke]]
Cetaceans have a [[cartilage|cartilaginous]] fluke at the end of their tails that is used for propulsion. The [[Tail fluke|fluke]] is set horizontally on the body and used with vertical movements, unlike fish and ichthyosaurs, which have vertical tails which move horizontally.<ref>{{Cite web|title=Why do whale and dolphin tails go up and down?|url=https://us.whales.org/whales-dolphins/why-do-whale-and-dolphin-tails-go-up-and-down/|access-date=2021-12-23|website=Whale & Dolphin Conservation USA|language=en-US}}</ref>