Editing Platypus (section)

== Description ==
In [[David Collins (lieutenant governor)|David Collins]]'s account of the new colony 1788–1801, he describes "an amphibious animal, of the mole species", with a drawing.<ref>{{cite book|url=https://archive.org/details/anaccountoftheen12668gut|title=An Account of the English Colony in New South Wales, Volume 2|first=David|last=Collins|access-date=5 July 2017|via=Internet Archive}}</ref>

The body and the broad, flat tail of the platypus are covered with dense, brown, biofluorescent [[fur]] that traps a layer of insulating air to keep the animal warm.<ref name="APC" /><ref name="ABRS" /><ref>{{cite journal |last1=Anich |first1=Paula Spaeth |title=Biofluorescence in the platypus (Ornithorhynchus anatinus) |journal=[[Mammalia (journal)|Mammalia]] |date=15 October 2020 |volume=85 |issue=2 |pages=179–181 |doi=10.1515/mammalia-2020-0027 |doi-access=free }}</ref> The fur is waterproof, and textured like that of a [[Mole (animal)|mole]].<ref>{{cite web |url=http://animal.discovery.com/mammals/platypus/ |title=Platypus: Facts, Pictures: Animal Planet |publisher=Animal.discovery.com |date=16 November 2011 |access-date=8 September 2012 |archive-date=27 July 2011 |archive-url=https://web.archive.org/web/20110727171511/http://animal.discovery.com/mammals/platypus/ |url-status=live }}</ref> The platypus's tail stores fat reserves, an adaptation also found in the [[Tasmanian devil]].<ref name="Guiler">{{cite book|author=Guiler, E.R.|year=1983|chapter=Tasmanian Devil|editor=R. Strahan|title=The Australian Museum Complete Book of Australian Mammals|pages=27–28|publisher=Angus & Robertson|isbn=978-0-207-14454-7}}</ref> [[webbed foot|Webbing]] is more significant on the front feet, which in land walking are folded up in [[knuckle-walking]] to protect the webbing.<ref name="Fish">{{cite journal |last1=Fish |first1=F. E. |last2=Frappell |first2=P. B. |last3=Baudinette |first3=R. V. |last4=Macfarlane |first4=P. M. |title=Energetics of Terrestrial Locomotion of the Platypus Ornithorhynchus Anatinus |journal=Journal of Experimental Biology |date=15 February 2001 |volume=204 |issue=4 |pages=797–803 |doi=10.1242/jeb.204.4.797 |pmid=11171362 |bibcode=2001JExpB.204..797F |hdl-access=free |hdl=2440/12192 }}</ref> The elongated snout and lower jaw are covered in soft skin, forming the bill. The nostrils are located on the snout's dorsal surface, while the eyes and ears are just behind the snout in a groove which closes underwater.<ref name="ABRS" /> Platypuses can give a low growl when disturbed, and a range of vocalisations have been reported in captivity.<ref name="APC" />

Size varies considerably in different regions, with average weight from {{convert|0.7|to|2.4|kg|lboz|abbr=on}}; males have average length {{convert|50|cm|in|0|abbr=on}}, while females are the smaller at {{convert|43|cm|in|frac=2|abbr=on}}.<ref name="ABRS" /> This variation does not seem to follow any particular climatic rule and may be due to other factors such as predation and human encroachment.<ref name="Workshop">{{cite web|url=http://www.medicine.utas.edu.au/research/mono/Taspaper.html|title=Current research on the platypus, ''Ornithorhynchus anatinus'' in Tasmania: Abstracts from the 1999 'Tasmanian Platypus Workshop'|author1=Munks, Sarah |author2=Nicol, Stewart |name-list-style=amp |publisher=University of Tasmania|date=May 1999| access-date = 23 October 2006|archive-url = https://web.archive.org/web/20060830075935/http://www.medicine.utas.edu.au/research/mono/Taspaper.html |archive-date = 30 August 2006|url-status=dead}}</ref>

The platypus has an average [[Core temperature|body temperature]] of about {{convert|32|C|F}}, lower than the {{convert|37|C|F}} typical of [[placentalia|placental mammals]].<ref name="DC">{{cite web|url=http://www.bio.davidson.edu/courses/anphys/1999/White/thermal.htm |title=Thermal Biology of the Platypus |publisher=Davidson College |year=1999 |access-date=14 September 2006 |url-status=dead |archive-url=https://web.archive.org/web/20120306024923/http://www.bio.davidson.edu/courses/anphys/1999/White/thermal.htm |archive-date=6 March 2012 }}</ref> Research suggests this has been a gradual adaptation to harsh environmental conditions among the few marginal surviving monotreme species, rather than a general characteristic of past monotremes.<ref name="temp">{{cite journal |last1=Watson |first1=Jm |last2=Graves |first2=Jam |title=Monotreme Cell-Cycles and the Evolution of Homeothermy |journal=Australian Journal of Zoology |date=1988 |volume=36 |issue=5 |pages=573 |doi=10.1071/ZO9880573 }}</ref><ref name="temp2">{{cite journal |last1=Dawson |first1=Tj |last2=Grant |first2=Tr |last3=Fanning |first3=D |title=Standard Metabolism of Monotremes and the Evolution of Homeothermy. |journal=Australian Journal of Zoology |date=1979 |volume=27 |issue=4 |pages=511 |doi=10.1071/ZO9790511 }}</ref>

In addition to laying eggs, the anatomy, [[ontogeny]], and genetics of monotremes shows traces of similarity to reptiles and birds. The platypus has a [[Reptile|reptilian]] gait with legs on the sides of the body, rather than underneath.<ref name="ABRS" /> The platypus's genes are a possible evolutionary link between the mammalian [[XY sex-determination system|XY]] and bird/reptile [[ZW sex-determination system|ZW]] sex-determination systems, as one of the platypus's five X chromosomes contains the [[DMRT1]] gene, which birds possess on their Z chromosome.<ref name="Graves">{{cite journal |last=Graves |first=Jennifer |date=10 March 2006 |title=Sex Chromosome Specialization and Degeneration in Mammals |journal=Cell |volume=124 |issue=5 |pages=901–914 |doi=10.1016/j.cell.2006.02.024 |pmid=16530039 |s2cid=8379688 |doi-access=free}}</ref>

As in all true mammals, the tiny bones that conduct sound in the [[middle ear]] are fully incorporated into the skull, rather than lying in the jaw as in pre-mammalian [[synapsid]]s. However, the external opening of the ear still lies at the base of the jaw.<ref name="ABRS" /> The platypus has extra bones in the shoulder girdle, including an [[interclavicle]] not found in other mammals.<ref name="ABRS" /> As in many other aquatic and semiaquatic [[vertebrates]], the bones show [[osteosclerosis]], increasing their density to provide ballast.<ref>{{Cite journal | doi = 10.1371/journal.pone.0059146|pmid=23565143|pmc=3615000| title = Bone Inner Structure Suggests Increasing Aquatic Adaptations in Desmostylia (Mammalia, Afrotheria)| journal = PLOS ONE| volume = 8| issue = 4| pages = e59146| year = 2013| last1 = Hayashi | first1 = S.| last2 = Houssaye | first2 = A.| last3 = Nakajima | first3 = Y.| last4 = Chiba | first4 = K.| last5 = Ando | first5 = T.| last6 = Sawamura | first6 = H.| last7 = Inuzuka | first7 = N.| last8 = Kaneko | first8 = N.| last9 = Osaki | first9 = T.|bibcode=2013PLoSO...859146H|doi-access=free}}</ref>

The platypus [[jaw]] is constructed differently from that of other mammals, and the jaw-opening muscle is different.<ref name="ABRS" /> Modern platypus young have three teeth in each of the [[maxilla]]e (one premolar and two [[Molar (tooth)|molars]]) and [[Mandible|dentaries]] (three molars), which they lose before or just after leaving the breeding burrow;<ref name="ABRS" /> adults instead develop heavily [[keratinisation|keratinised]] food-grinding pads called [[ceratodontes]].<ref name="ABRS" /><ref name="Piper-2007" /><ref name="Haeckel1895">{{cite book |last=Haeckel |url=https://books.google.com/books?id=AOi2AAAAIAAJ&pg=PA142 |title=Systematische Phylogenie der Wirbelthiere (Vertebrata) |publisher=Georg Reimer |year=1895 |edition=1 |series=Entwurf einer systematischen Stammesgeschichte |volume=3 |location=Berlin |pages=142–143 |language=de |access-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716071006/https://books.google.com/books?id=AOi2AAAAIAAJ&pg=PA142 |archive-date=16 July 2021 |url-status=live}}</ref> The first upper and third lower cheek teeth of platypus nestlings are small, each having one principal cusp, while the other teeth have two main cusps.<ref>{{cite book |last=Ungar |first=Peter S. |title=Mammal Teeth: Origin, Evolution, and Diversity |publisher=The Johns Hopkins University Press |year=2010 |isbn=978-0-801-89668-2 |page=130 |chapter=Monotremata and Marsupialia}}</ref>

<gallery mode="packed" heights="180px">
Duck-billed platypus (Ornithorhynchus anatinus) diving Scottsdale.jpg|Diving
Duck-billed platypus (Ornithorhynchus anatinus) surfacing Scottsdale.jpg|Surfacing
Duck-billed platypus (Ornithorhynchus anatinus) Scottsdale 4.jpg
</gallery>

=== Venom ===
{{Main|Platypus venom}}
[[File:Platypus spur.JPG|right|thumb|The calcaneus spur on the male's hind limb is used to inject venom.]]

While both male and female platypuses are born with back ankle spurs, only the males' deliver venom.<ref>{{cite web |url=http://www.australianfauna.com/platypus.php |title=Australian Fauna |publisher=Australian Fauna |access-date=14 May 2010 |url-status=dead |archive-url=https://web.archive.org/web/20120529040439/http://www.australianfauna.com/platypus.php |archive-date=29 May 2012 }}</ref><ref>{{cite web |url=http://www.usyd.edu.au/news/84.html?newsstoryid=2267 |title=Platypus venom linked to pain relief |publisher=University of Sydney |date=8 May 2008 |access-date=14 May 2010 |archive-date=21 August 2011 |archive-url=https://web.archive.org/web/20110821151157/http://www.usyd.edu.au/news/84.html?newsstoryid=2267 |url-status=live }}</ref><ref>{{cite web |url=http://rainforest-australia.com/platypus_poison.htm |title=Platypus poison |publisher=Rainforest Australia |access-date=14 May 2010 |url-status=dead |archive-url=https://web.archive.org/web/20100529165453/http://rainforest-australia.com/platypus_poison.htm |archive-date=29 May 2010 }}</ref>
It is powerful enough to kill smaller animals such as dogs, and though it is not lethal to humans, it can inflict weeks of agony.<ref name="PS" /><ref>Weimann, Anya (4 July 2007) [https://web.archive.org/web/20121105043922/http://www.cosmosmagazine.com/news/1423/evolution-platypus-venom-revealed Evolution of platypus venom revealed]. ''[[Cosmos (magazine)|Cosmos]]''.</ref> [[Edema]] rapidly develops around the wound and gradually spreads through the affected limb, and it may develop into an excruciating [[hyperalgesia]] (heightened sensitivity to pain) persisting for days or even months.<ref name="JN">{{cite journal |author=de Plater, G.M. |author2=Milburn, P.J. |author3=Martin, R.L. |year=2001 |title=Venom From the Platypus, ''Ornithorhynchus anatinus'', Induces a Calcium-Dependent Current in Cultured Dorsal Root Ganglion Cells |journal=Journal of Neurophysiology |volume=85 |issue=3 |pages=1340–5 |doi=10.1152/jn.2001.85.3.1340 |pmid=11248005 |s2cid=2452708 }}</ref><ref name="venom">{{cite web |title=The venom of the platypus (''Ornithorhynchus anatinus'') |url=http://www.kingsnake.com/toxinology/old/mammals/platypus.html |url-status=dead |archive-url=https://web.archive.org/web/20120201185504/http://www.kingsnake.com/toxinology/old/mammals/platypus.html |archive-date=1 February 2012 |access-date=13 September 2006}}</ref>

The venom is composed largely of [[defensin]]-like [[protein]]s (DLPs) produced by the immune system, three of which are unique to the platypus.<ref name="PS">{{cite journal| last = Gerritsen| first = Vivienne Baillie| title = Platypus poison| journal = Protein Spotlight| issue = 29| date = December 2002| url = http://www.expasy.org/spotlight/back_issues/sptlt029.shtml| access-date = 14 September 2006| archive-date = 20 October 2008| archive-url = https://web.archive.org/web/20081020054110/http://www.expasy.org/spotlight/back_issues/sptlt029.shtml| url-status = live}}</ref> In other animals, defensins [[lysis|kill]] pathogenic bacteria and viruses, but in platypuses they are also collected into a venom against predators. Venom is produced in the [[wikt:crural|crural]] glands of the male, which are kidney-shaped [[alveolar gland]]s connected by a thin-walled duct to a [[calcaneus]] spur on each hind limb. The female platypus, in common with echidnas, has rudimentary spur buds that do not develop (dropping off before the end of their first year) and lack functional crural glands.<ref name="ABRS" /> Venom production rises among males during the breeding season, and it may be used to assert dominance.<ref name="PS" />

Similar spurs are found on many archaic mammal groups, indicating that this was an ancient general characteristic among mammals.<ref>Jørn H. Hurum, Zhe-Xi Luo, and Zofia Kielan-Jaworowska, 
Were mammals originally venomous?, Acta Palaeontologica Polonica 51 (1), 2006: 1–11</ref>

=== Electrolocation ===
[[File:Platypus electrolocation.svg|thumb|upright=2<!--for readability of svg text-->|The platypus has secondarily acquired [[Electroreception and electrogenesis|electroreception]]. Its receptors are arranged in stripes on its bill, giving it high sensitivity to the sides and below; it makes quick turns of its head as it swims to detect prey.<ref name="Electro1"/>]]

[[Monotremes]] are the only mammals (apart from the [[Guiana dolphin]])<ref>{{cite journal |last1=Czech-Damal |first1=Nicole U. |last2=Liebschner |first2=Alexander |last3=Miersch |first3=Lars |last4=Klauer |first4=Gertrud |last5=Hanke |first5=Frederike D. |last6=Marshall |first6=Christopher |last7=Dehnhardt |first7=Guido |last8=Hanke |first8=Wolf |date=22 February 2012 |title=Electroreception in the Guiana dolphin (Sotalia guianensis) |journal=Proceedings of the Royal Society B: Biological Sciences |volume=279 |issue=1729 |pages=663–668 |doi=10.1098/rspb.2011.1127 |pmc=3248726 |pmid=21795271}}</ref> known to have a sense of [[electroreception]], and the platypus's electroreception is the most sensitive of any monotreme.<ref>{{cite journal |last1=Proske |first1=Uwe |last2=Gregory |first2=J. E. |last3=Iggo |first3=A. |year=1998 |title=Sensory receptors in monotremes |journal=Philosophical Transactions of the Royal Society of London |volume=353 |issue=1372 |pages=1187–1198 |doi=10.1098/rstb.1998.0275 |pmc=1692308 |pmid=9720114}}</ref><ref name="Electro1">{{cite journal |last=Pettigrew |first=John D. |year=1999 |title=Electroreception in Monotremes |url=http://jeb.biologists.org/cgi/reprint/202/10/1447.pdf |url-status=live |journal=The Journal of Experimental Biology |volume=202 |issue=Part 10 |pages=1447–54 |doi=10.1242/jeb.202.10.1447 |pmid=10210685 |archive-url=https://web.archive.org/web/20060928054253/http://jeb.biologists.org/cgi/reprint/202/10/1447.pdf |archive-date=28 September 2006 |access-date=19 September 2006 |doi-access=free|bibcode=1999JExpB.202.1447P }}</ref> Feeding by neither sight nor smell,<ref name="draft_genome" /> the platypus closes its eyes, ears, and nose when it dives.<ref>{{cite journal |author=Gregory, J.E. |author2=Iggo, A. |author3=McIntyre, A.K. |author4=Proske, U. |date=June 1988 |title=Receptors in the Bill of the Platypus |journal=Journal of Physiology |volume=400 |issue=1 |pages=349–366 |doi=10.1113/jphysiol.1988.sp017124 |pmc=1191811 |pmid=3418529}}</ref> Digging in the bottom of streams with its bill, its electroreceptors detect tiny electric currents generated by the muscular contractions of its prey, enabling it to distinguish between animate and inanimate objects.<ref name="Electro1" /> Experiments have shown the platypus will even react to an "artificial shrimp" if a small electric current is passed through it.<ref name="Manning">{{cite book |author1=Manning, A. |url=https://archive.org/details/introductiontoan0000mann_m2z8 |title=An Introduction to Animal Behaviour |author2=Dawkins, M.S. |publisher=Cambridge University Press |year=1998 |edition=5th |url-access=registration}}</ref>

The [[electroreceptor]]s are located in rostrocaudal rows in the skin of the bill, while [[mechanoreceptor]]s for touch are uniformly distributed across the bill. The electrosensory area of the [[cerebral cortex]] is in the tactile [[somatosensory]] area, and some cortical cells receive input from both electroreceptors and mechanoreceptors, suggesting the platypus feels electric fields like touches. These receptors in the bill dominate the [[somatotopic map]] of the platypus brain, in the same way human hands dominate the [[Cortical homunculus|Penfield homunculus map]].<ref name="sensory_platypus">{{cite journal |last1=Pettigrew |first1=John D. |first2=P. R. |last2=Manger |first3=S. L. |last3=Fine |title=The sensory world of the platypus |journal=Philosophical Transactions of the Royal Society of London |pages=1199–1210 |issue=1372 |year=1998 |pmid=9720115|pmc=1692312 |doi=10.1098/rstb.1998.0276 |volume=353 }}</ref><ref name="Ancestors_Tale">{{cite book |first=Richard |last=Dawkins |author-link=Richard Dawkins |title=The Ancestor's Tale, A Pilgrimage to the Dawn of Life |chapter=The Duckbill's Tale |publisher=Houghton Mifflin |location=Boston, Massachusetts |year=2004 |isbn=978-0-618-00583-3 |title-link=The Ancestor's Tale }}</ref>

The platypus can feel the direction of an electric source, perhaps by comparing differences in [[signal strength]] across the sheet of electroreceptors, enhanced by the characteristic side-to-side motion of the animal's head while hunting. It may also be able to determine the distance of moving prey from the time lag between their electrical and mechanical pressure pulses.<ref name="Electro1" />

Monotreme electrolocation for hunting in murky waters may be tied to their tooth loss.<ref name="Masakazu Asahara 2016">Masakazu Asahara; Masahiro Koizumi; Thomas E. Macrini; Suzanne J. Hand; Michael Archer (2016). "Comparative cranial morphology in living and extinct platypuses: Feeding behavior, electroreception, and loss of teeth". Science Advances. 2 (10): e1601329. {{doi|10.1126/sciadv.1601329}}.</ref> The extinct ''[[Obdurodon]]'' was electroreceptive, but unlike the modern platypus it foraged [[pelagic zone|pelagically]].<ref name="Masakazu Asahara 2016" />

=== Eyes ===
In recent studies it has been suggested that the eyes of the platypus are more similar to those of [[Pacific hagfish]] or Northern Hemisphere [[lamprey]]s than to those of most tetrapods. The eyes also contain [[Double cone (biology)|double cones]], unlike most mammals.<ref>{{cite journal |last1=Zeiss|first1=Caroline|title=Comparative retinal morphology of the platypus|doi=10.1002/jmor.10959 |year=2011 |first2=Ivan R. |last3=Murphy|first3=Christopher J. |last4=Dubielzig|first4=Richard W. |journal=Journal of Morphology |volume=272 |issue=8 |pages=949–57 |pmid=21567446|last2=Schwab|s2cid=28546474}}</ref>

Although the platypus's eyes are small and not used under water, several features indicate that vision was important for its ancestors. The [[cornea]]l surface and the adjacent surface of the lens is flat, while the posterior surface of the lens is steeply curved, similar to the eyes of other aquatic mammals such as otters and sea-lions. A [[Temporal bone|temporal]] (ear side) concentration of [[retinal ganglion cell]]s, important for binocular vision, indicates a vestigial role in [[predation]], though the actual visual acuity is insufficient for such activities. Limited acuity is matched by low [[cortical magnification]], a small [[lateral geniculate nucleus]], and a large [[optic tectum]], suggesting that the [[Midbrain tectum|visual midbrain]] plays a more important role than the [[visual cortex]], as in some rodents. These features suggest that the platypus has adapted to an aquatic and nocturnal lifestyle, developing its electrosensory system at the cost of its visual system. This contrasts with the small number of electroreceptors in the [[short-beaked echidna]], which dwells in dry environments, while the [[long-beaked echidna]], which lives in moist environments, is intermediate between the other two monotremes.<ref name="sensory_platypus" />

=== Biofluorescence ===
In 2020, research revealed that platypus fur gives a bluish-green [[biofluorescent]] glow in [[Blacklight|black light]].<ref>{{cite web|last=November 2020|first=Mindy Weisberger-Senior Writer 02|title=Platypuses glow an eerie blue-green under UV light|url=https://www.livescience.com/platypuses-glow-uv-light.html|access-date=7 November 2020|website=livescience.com|date=2 November 2020 |language=en|archive-date=5 November 2020|archive-url=https://web.archive.org/web/20201105063117/https://www.livescience.com/platypuses-glow-uv-light.html|url-status=live}}</ref>