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=== Whales === [[File:Toothed whale sound production.svg|thumb|upright=1.8|right |Diagram illustrating sound generation, propagation and reception in a toothed whale. Outgoing sounds are cyan and incoming ones are green.]] Biosonar is valuable to both [[toothed whales]] (suborder [[Odontoceti]]), including [[dolphin]]s, [[porpoise]]s, [[river dolphin]]s, [[killer whale]]s and [[sperm whale]]s, and [[baleen whales]] (suborder [[Mysticeti]]), including [[right whales|right]], [[bowhead whales |bowhead]], [[pygmy right whales |pygmy right]], and [[gray whales]] and [[rorquals]], because they live in an underwater habitat that has favourable acoustic characteristics and where [[visual perception |vision]] is often extremely limited in range due to absorption or [[turbidity]].<ref>{{cite book |last1=Hughes |first1=H. C. |title=Sensory Exotica: A World Beyond Human Experience |date=1999 |publisher=A Bradford Book |location=Cambridge, Massachusetts}}</ref> [[Odontocetes]] are generally able to hear sounds at [[ultrasonic]] frequencies while [[mysticetes]] hear sounds within the [[infrasonic]] frequency regime.<ref name="Viglino 2021">{{cite journal |last1=Viglino |first1=M. |last2=GaetΓ‘n |first2=M. |last3=Buono |first3=M. R. |last4=Fordyce |first4=R. E. |last5=Park |first5=T. |title=Hearing from the ocean and into the river: the evolution of the inner ear of Platanistoidea (Cetacea: Odontoceti) |journal=Paleobiology |date=2021 |volume=47 |issue=4 |pages=591β611 |doi=10.1017/pab.2021.11 | bibcode=2021Pbio...47..591V |s2cid=233517623 |url=https://zenodo.org/record/4480277 }}</ref> ==== Whale evolution ==== [[Cetacea]]n evolution consisted of three main [[Evolutionary radiation|radiations]]. Throughout the middle and late [[Eocene]] periods (49-31.5 million years ago), [[archaeocete]]s, primitive toothed Cetacea that arose from terrestrial mammals, were the only cetaceans.<ref name="Gatesy Geisler Chang 2012">{{cite journal |last1=Gatesy |first1=John |last2=Geisler |first2=Jonathan H. |last3=Chang |first3=Joseph |author4=Buell, Carl |author5=Berta, Annalisa |author6=Meredith, Robert W. |author7=Springer, Mark S. |author8=McGowen, Michael R. |display-authors=3 |year=2012 |title=A phylogenetic blueprint for a modern whale |journal=[[Molecular Phylogenetics and Evolution]] |volume=66 |issue=2 |pages=479β506 |doi=10.1016/j.ympev.2012.10.012 |pmid=23103570}}</ref><ref name="Fordyce 1980">{{cite journal |last1=Fordyce |first1=R. E. |year=1980 |title=Whale evolution and oligocene southern-ocean environments | journal= Palaeogeography, Palaeoclimatology, Palaeoecology |volume=31 |pages=319β336 |doi=10.1016/0031-0182(80)90024-3 |bibcode=1980PPP....31..319F |doi-access=free }}</ref> They did not echolocate, but had slightly adapted underwater hearing.<ref name="Fordyce 2003">{{cite book |last=Fordyce |first=R. E. |year=2003 |chapter=Cetacean Evolution and Eocene-Oligocene oceans revisited |editor1=Prothero, Donald R. |editor2=Ivany, Linda C. |editor3=Nesbitt, Elizabeth A. |title=From Greenhouse to Icehouse: the Marine Eocene-Oligocene Transition |publisher=[[Columbia University Press]] |pages=154β170 |isbn=978-0-2311-2716-5}}</ref> By the late middle Eocene, acoustically isolated ear bones had evolved to give [[Basilosauridae|basilosaurid]] archaeocetes directional underwater hearing at low to mid frequencies.<ref name="Lindberg 2007">{{cite journal |last1=Lindberg |first1=D. R. |last2=Pyenson |first2=Nicholas D. |author2-link=Nicholas Pyenson |year=2007 |title=Things that go bump in the night: evolutionary interactions between cephalopods and cetaceans in the tertiary |journal=Lethaia |volume=40 |issue=4 | pages=335β343 |doi=10.1111/j.1502-3931.2007.00032.x|bibcode=2007Letha..40..335L }}</ref> With the extinction of archaeocetes at the onset of the [[Oligocene]] (33.9β23 million years ago), two new lineages evolved in a second radiation. Early mysticetes (baleen whales) and odontocetes appeared in the middle Oligocene in New Zealand.<ref name="Fordyce 1980"/> Extant odontocetes are [[monophyletic]] (a single evolutionary group), but echolocation evolved twice, convergently: once in ''[[Xenorophus]]'', an Oligocene [[Stem-group|stem]] odontocete, and once in the [[crown group|crown]] odontocetes.<ref name="Racicot 2019">{{cite journal |last1=Racicot |first1=Rachel A. |last2=Boessenecker |first2=Robert W. |last3=Darroch |first3=Simon A. F. |last4=Geisler |first4=Jonathan H. |year=2019 |title=Evidence for convergent evolution of ultrasonic hearing in toothed whales |journal=Biology Letters |volume=15 |issue=5 |pages=20190083 |doi=10.1098/rsbl.2019.0083 |pmid=31088283 |s2cid=155091623 |pmc=6548736 }}</ref> {{clade |label1=<!--<ref name="Gatesy Geisler Chang 2012"/>--> |1={{clade |label1=[[Cetacea]] |1={{clade |label2='''''directional u/water hearing''''' |sublabel2=''mid/late [[Eocene]]'' |2=[[Basilosauridae]] β |1={{clade |label1=[[Odontoceti]] |sublabel1=''[[Oligocene]]'' |1={{clade |label1='''''echolocation''''' |sublabel1=''late [[Oligocene]]'' |1=''[[Xenorophus]]'' β |label2='''''echolocation''''' |2={{clade |1=[[Physeteroidea]] |2={{clade |1=[[Ziphiidae]], etc. |label2=''adaptive radiation'' |sublabel2=''[[Miocene]]'' |2=[[Delphinoidea]] }} }} }} |label2='''''echolocation''''' |sublabel2=''middle [[Oligocene]]'' |2=[[Mysticeti]] }} }} }} }} {| style="font-size: 10px; background: whitesmoke; float:right;" |+ style="font-size:12px;" | '''Cetacean evolution timeline'''<ref name="Fordyce 1980"/> |- style="background:lightgray;" ! scope="col" style="width: 50px;" | Epoch ! scope="col" style="width: 55px;" | Start date ! scope="col" style="width: 100px;" | Event |- | [[Miocene]] || 23 [[Myr|mya]] || [[Adaptive radiation]], esp. of dolphins |- | [[Oligocene]] || 34 mya || [[Odontocetes]] echolocation |- | [[Eocene]] || 49 mya || [[Archaeoceti|Archaeocetes]] underwater hearing |} Physical restructuring of the oceans has played a role in the evolution of echolocation. Global cooling at the [[Eocene-Oligocene boundary]] caused a change from a [[Greenhouse and icehouse Earth|greenhouse to an icehouse world]]. Tectonic openings created the [[Southern Ocean]] with a free flowing [[Antarctic Circumpolar Current]].<!--<ref name="Fordyce 1980"/>--><ref name="Fordyce 2003"/><ref name="Lindberg 2007"/><ref name="Steeman_2009">{{cite journal |last1=Steeman |first1=Mette E. |last2=Hebsgaard |first2=Martin B. |last3=Fordyce |first3=R. Ewan |last4=Ho |first4=Simon Y. W. |last5=Rabosky |first5=Daniel L. |last6=Nielsen |first6=Rasmus |last7=Rahbek |first7=Carsten |last8=Glenner |first8=Henrik |last9=SΓΈrensen |first9=Martin V. |last10=Willerslev |first10=Eske |display-authors=3 |title=Radiation of extant cetaceans driven by restructuring of the oceans |journal=Systematic Biology |volume=58 |issue=6 |pages=573β585 |date=December 2009 |pmid=20525610 |pmc=2777972 |doi=10.1093/sysbio/syp060 }}</ref> These events encouraged selection for the ability to locate and capture prey in turbid river waters, which enabled the odontocetes to invade and feed at depths below the [[photic zone]]. In particular, echolocation below the photic zone could have been a predation adaptation to [[Diel vertical migration|diel migrating]] [[cephalopods]].<ref name="Lindberg 2007"/><ref>{{cite journal |last1=Fordyce |first1=R. Ewan |last2=Barnes |first2=Lawrence G. |year=1994 |title=The evolutionary history of whales and dolphins | journal=Annual Review of Earth and Planetary Sciences |volume=22 |issue=1 | pages=419β455 |doi=10.1146/annurev.ea.22.050194.002223 | bibcode=1994AREPS..22..419F }}</ref> The family [[Delphinidae]] (dolphins) diversified in the [[Neogene]] (23β2.6 million years ago), evolving extremely specialized echolocation.<ref>{{cite journal | last1=McGowen |first1=Michael R. |last2=Spaulding |first2=Michelle |last3=Gatesy |first3=John |title=Divergence date estimation and a comprehensive molecular tree of extant cetaceans |journal=Molecular Phylogenetics and Evolution |volume=53 |issue=3 |pages=891β906 |date=December 2009 |pmid=19699809 |doi=10.1016/j.ympev.2009.08.018 }}</ref><ref name="Fordyce 2003"/> Four proteins play a major role in toothed whale echolocation. [[Prestin]], a motor protein of the outer hair cells of the inner ear of the mammalian [[cochlea]], is associated with hearing sensitivity.<ref name="Liu Rossiter Xiuqun 2010">{{cite journal | last1=Liu |first1=Yang |last2=Rossiter |first2=Stephen J. |last3=Han |first3=Xiuqun |last4=Cotton |first4=James A. |last5=Zhang |first5=Shuyi |title=Cetaceans on a molecular fast track to ultrasonic hearing |journal=Current Biology |volume=20 |issue=20 |pages=1834β1839 |date=October 2010 |pmid=20933423 |doi=10.1016/j.cub.2010.09.008 |doi-access=free |bibcode=2010CBio...20.1834L }}</ref> It has undergone two clear episodes of accelerated evolution in cetaceans.<ref name="Liu Rossiter Xiuqun 2010"/> The first is connected to odontocete divergence, when echolocation first developed, and the second with the increase in echolocation frequency among dolphins. [[TMC1|Tmc1]] and Pjvk are proteins related to hearing sensitivity: Tmc1 is associated with hair cell development and high-frequency hearing, and Pjvk with hair cell function.<ref name="Davies Cotton Kirwan 2012">{{Cite journal |last1=Davies |first1=K. T. J. |last2=Cotton |first2=J. A. |last3=Kirwan |first3=J. D. |last4=Teeling |first4=E. C. |last5=Rossiter |first5=S. J. |date=May 2012 |title=Parallel signatures of sequence evolution among hearing genes in echolocating mammals: an emerging model of genetic convergence |journal=Heredity |volume=108 |issue=5 |pages=480β489 |doi=10.1038/hdy.2011.119 |issn=1365-2540 |pmc=3330687 |pmid=22167055}}</ref> [[Molecular evolution]] of Tmc1 and Pjvk indicates positive selection for echolocation in odontocetes.<ref name="Davies Cotton Kirwan 2012"/> [[CLDN14|Cldn14]], a member of the tight junction proteins which form barriers between inner ear cells, shows the same evolutionary pattern as Prestin.<ref>{{cite journal | last1=Xu |first1=Huihui |last2=Liu |first2=Yang |last3=He |first3=Guimei |last4=Rossiter |first4=Stephen J. |last5=Zhang |first5=Shuyi |title=Adaptive evolution of tight junction protein claudin-14 in echolocating whales |journal=Gene |volume=530 |issue=2 |pages=208β214 |date=November 2013 |pmid=23965379 |doi=10.1016/j.gene.2013.08.034 }}</ref> The two events of protein evolution, for Prestin and Cldn14, occurred at the same times as the tectonic opening of the [[Drake Passage]] (34β31 Ma) and Antarctic ice growth at the Middle [[Miocene]] climate transition (14 Ma), with the divergence of odontocetes and mysticetes occurring with the former, and the speciation of Delphinidae with the latter.<ref name="Steeman_2009"/> The evolution of two cranial structures may be linked to echolocation. Cranial telescoping (overlap between [[Frontal bone|frontal]] and [[maxilla]]ry bones, and rearwards displacement of the nostrils<ref name="Roston Roth 2019">{{cite journal | last1=Roston | first1=Rachel A. | last2=Roth | first2=V. Louise | title=Cetacean Skull Telescoping Brings Evolution of Cranial Sutures into Focus | journal=The Anatomical Record | publisher=Wiley | volume=302 | issue=7 | date=8 March 2019 | issn=1932-8486 | doi=10.1002/ar.24079 | pages=1055β1073| pmid=30737886 | pmc=9324554 }}</ref>) developed first in [[Xenorophidae|xenorophids]]. It evolved further in stem odontocetes, arriving at full cranial telescoping in the crown odontocetes.<ref name="Churchill Geisler Beatty 2018">{{Cite journal |last1=Churchill |first1=Morgan |last2=Geisler |first2=Jonathan H. |last3=Beatty |first3=Brian L. |last4=Goswami |first4=Anjali |date=2018 |title=Evolution of cranial telescoping in echolocating whales (Cetacea: Odontoceti) |url=https://onlinelibrary.wiley.com/doi/abs/10.1111/evo.13480 |journal=Evolution |volume=72 |issue=5 |pages=1092β1108 |doi=10.1111/evo.13480 |pmid=29624668 |s2cid=4656605 |issn=1558-5646|url-access=subscription }}</ref> Movement of the nostrils may have allowed for a larger nasal apparatus and [[Melon (cetacean)|melon]] for echolocation.<ref name="Churchill Geisler Beatty 2018"/> This change occurred after the divergence of the neocetes from the basilosaurids.<ref name="Coombs Clavel Park 2020">{{Cite journal |last1=Coombs |first1=Ellen J. |last2=Clavel |first2=Julien |last3=Park |first3=Travis |last4=Churchill |first4=Morgan |last5=Goswami |first5=Anjali |date=2020-07-10 |title=Wonky whales: the evolution of cranial asymmetry in cetaceans |journal=BMC Biology |volume=18 |issue=1 |page=86 |doi=10.1186/s12915-020-00805-4 |issn=1741-7007 |pmc=7350770 |pmid=32646447 |doi-access=free }}</ref> The first shift towards cranial asymmetry occurred in the Early Oligocene, prior to the xenorophids.<ref name="Coombs Clavel Park 2020"/> A xenorophid fossil (''Cotylocara macei'') has cranial asymmetry, and shows other indicators of echolocation.<ref name="Geisler Colbert Carew 2014">{{Cite journal |last1=Geisler |first1=Jonathan H. |last2=Colbert |first2=Matthew W. |last3=Carew |first3=James L. |date=April 2014 |title=A new fossil species supports an early origin for toothed whale echolocation |url=https://www.nature.com/articles/nature13086 |journal=Nature |volume=508 |issue=7496 |pages=383β386 |doi=10.1038/nature13086 |pmid=24670659 |bibcode=2014Natur.508..383G |s2cid=4457391 |issn=1476-4687|url-access=subscription }}</ref> However, basal xenorophids lack cranial asymmetry, indicating that this likely evolved twice.<ref name="Coombs Clavel Park 2020"/> Extant odontocetes have asymmetric nasofacial regions; generally, the [[median plane]] is shifted to the left and structures on the right are larger.<ref name="Geisler Colbert Carew 2014"/> Both cranial telescoping and asymmetry likely relate to sound production for echolocation.<ref name="Churchill Geisler Beatty 2018"/> ==== Mechanism ==== [[File:Killer whale residents broadband.ogg |left|thumb|Southern Alaskan resident [[killer whale]]s using echolocation]] Thirteen species of extant odontocetes [[convergently evolved]] narrow-band high-frequency (NBHF) echolocation in four separate events. These species include the families [[Kogiidae]] (pygmy sperm whales) and [[Phocoenidae]] (porpoises), as well as some species of the genus ''[[Lagenorhynchus]]'', all of ''[[Cephalorhynchus]]'', and the [[La Plata dolphin]]. NBHF is thought to have evolved as a means of predator evasion; NBHF-producing species are small relative to other odontocetes, making them viable prey to large species such as the [[orca]]. However, because three of the groups developed NBHF prior to the emergence of the orca, predation by other ancient raptorial odontocetes must have been the driving force for the development of NBHF, not predation by the orca. Orcas, and, presumably ancient raptorial odontocetes such as ''Acrophyseter'', are unable to hear frequencies above 100 kHz.<ref>{{cite journal |last1=Galatius |first1=Anders |last2=Olsen |first2=Morten Tange |last3=Steeman |first3=Mette Elstrup |last4=Racicot |first4=Rachel A. |last5=Bradshaw |first5=Catherine D. |last6=Kyhn |first6=Line A. |last7=Miller |first7=Lee A. |title=Raising your voice: evolution of narrow-band high-frequency signals in toothed whales (Odontoceti) |journal=Biological Journal of the Linnean Society |volume=166 |issue= 2 |pages=213β224 |date=2019 |doi=10.1093/biolinnean/bly194 |hdl=1983/dc8d8192-b8b6-4ec3-abd5-2ef84fddbee8 |hdl-access=free }}</ref> Another reason for variation in echolocation is habitat. For all sonar systems, the limiting factor deciding whether a returning echo is detected is the echo-to-noise ratio (ENR). The ENR is given by the emitted source level (SL) plus the target strength, minus the two-way transmission loss (absorption and spreading) and the received noise.<ref name="Kyhn, L.A. 2010">{{cite journal |last1=Kyhn |first1=L. A. |last2=Jensen |first2=F. H. |last3=Beedholm |first3=K. |last4=Tougaard |first4=J. |last5=Hansen |first5=M. |last6=Madsen |first6=P. T. |title=Echolocation in sympatric Peale's dolphins (''Lagenorhynchus australis'') and Commerson's dolphins (''Cephalorhynchus commersonii'') producing narrow-band high-frequency clicks |journal=The Journal of Experimental Biology |volume=213 |issue=11 |pages=1940β1949 |date=June 2010 |pmid=20472781 |doi=10.1242/jeb.042440 |doi-access=free }}</ref> Animals will adapt either to maximize range under noise-limited conditions (increase source level) or to reduce noise clutter in a shallow and/or littered habitat (decrease source level). In cluttered habitats, such as coastal areas, prey ranges are smaller, and species such as [[Commerson's dolphin]] (''Cephalorhynchus commersonii'') have lowered source levels to better suit their environment.<ref name="Kyhn, L.A. 2010" /> {{Anchor |Mechanics of echolocation in whales}} Toothed whales emit a focused beam of high-frequency clicks in the direction that their head is pointing. Sounds are generated by passing air from the bony nares through the [[Whale_vocalization#Odontocete_whales|phonic lips]]. These sounds are reflected by the dense concave bone of the cranium and an air sac at its base. The focused beam is modulated by a large fatty organ known as the melon. This acts like an acoustic lens because it is composed of lipids of differing densities. Most toothed whales use clicks in a series, or click train, for echolocation, while the sperm whale may produce clicks individually. Toothed whale whistles do not appear to be used in echolocation. Different rates of click production in a click train give rise to the familiar barks, squeals and growls of the [[bottlenose dolphin]]. A click train with a repetition rate over 600 per second is called a burst pulse. In bottlenose dolphins, the auditory brain response resolves individual clicks up to 600 per second, but yields a graded response for higher repetition rates.<ref>{{cite book |last=Cranford |first=T. W. |chapter=In Search of Impulse Sound Sources in Odontocetes |date=2000 |title=Hearing by Whales and Dolphins |series=Springer Handbook of Auditory Research series |volume=12 |pages=109β155 |editor1=Au, W. W. |editor2=Popper, A. N. |editor3=Fay, R. R. |publisher=Springer |location=New York |doi=10.1007/978-1-4612-1150-1_3 |isbn=978-1-4612-7024-9 }}</ref> It has been suggested that the arrangement of the teeth of some smaller toothed whales may be an adaptation for echolocation.<ref>{{cite journal |last=Dobbins |first=P. |title=Dolphin sonar--modelling a new receiver concept |journal=Bioinspiration & Biomimetics |volume=2 |issue=1 |pages=19β29 |date=March 2007 |pmid=17671323 |doi=10.1088/1748-3182/2/1/003 |url=http://biomimetic.pbworks.com/f/Dolphin+sonar%E2%80%94modelling+a+new+receiverDobbins.pdf |bibcode=2007BiBi....2...19D |s2cid=27290079 }}</ref> The teeth of a bottlenose dolphin, for example, are not arranged symmetrically when seen from a vertical plane. This asymmetry could possibly be an aid in sensing if echoes from its biosonar are coming from one side or the other; but this has not been tested experimentally.<ref>{{cite book |last1=Goodson |first1=A. D. |last2=Klinowska |first2=M. A. |date=1990 |chapter=A proposed echolocation receptor for the bottlenose dolphin (''Tursiops truncatus''): modeling the receive directivity from tooth and lower jaw geometry |title=Sensory Abilities of Cetaceans |volume=196 |editor1=Thomas, J. A. |editor2=Kastelein, R. A. |location=New York |publisher=Plenum |pages=255β267 |series=NATO ASI Series A }}</ref> 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. Lateral sound may be received through 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 quietening the emitted sound. In bats this is known to happen, but here the hearing sensitivity is also reduced close to a target.<ref>{{cite book |last=Ketten |first=D. R. |date=1992 |chapter=The Marine Mammal Ear: Specializations for aquatic audition and echolocation |title=The Evolutionary Biology of Hearing |url=https://archive.org/details/evolutionarybiol0000unse_r3h2 |url-access=registration |editor1=Webster, D. |editor2=Fay, R. |editor3=Popper, A. |publisher=Springer-Verlag |pages=[https://archive.org/details/evolutionarybiol0000unse_r3h2/page/717 717]β750 }}</ref><ref>{{cite book |last=Ketten |first=D. R. |date=2000 |chapter=Cetacean Ears |title=Hearing by Whales and Dolphins |editor1=Au, W. W. |editor2=Popper, A. N. |editor3=Fay, R. R. |series=SHAR Series for Auditory Research |publisher=Springer |pages=43β108 }}</ref>
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