Editing Cetacea (section)

=== 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>