變更

==特徵==

長成的鴨嘴獸的體重0.7～2.4公斤（1.5～5.3英磅)。雄鸭嘴兽比雌性大，雄性体长平均50公分（20英寸），而雌性则为 43公分（17英寸），不同地区间体型差异也有较大变化<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  |lastauthoramp=yes |publisher=University of Tasmania|date=May 1999| accessdate = 23 October 2006|archiveurl = https://web.archive.org/web/20060830075935/http://www.medicine.utas.edu.au/research/mono/Taspaper.html |archivedate = 30 August 2006|deadurl=yes}}</ref>。其体温在32 °C（90 °F）左右<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 |accessdate=14 September 2006 |deadurl=yes |archiveurl=https://web.archive.org/web/20120306024923/http://www.bio.davidson.edu/courses/anphys/1999/White/thermal.htm |archivedate=6 March 2012 }}</ref><ref name="temp">{{cite journal|journal=Australian Journal of Zoology|title=Monotreme Cell-Cycles and the Evolution of Homeothermy|author=Watson, J.M. |author2=Graves, J.A.M. |volume=36|issue=5|pages=573–584|year=1988|publisher=CSIRO | doi = 10.1071/ZO9880573}}</ref><ref name="temp2">{{cite journal|journal=Australian Journal of Zoology|title=Standard Metabolism of Monotremes and the Evolution of Homeothermy|author= Dawson, T.J.|author2= Grant, T.R.|author3= Fanning, D. |volume=27|issue=4|pages=511–5|year=1979|publisher=CSIRO | doi = 10.1071/ZO9790511}}</ref>。由於沒有明顯的[[奶頭]]，剛孵化的鴨嘴獸須尋找母獸腹部泌乳孔吸吮乳汁維生。与[[袋獾]]一样，其粗大的尾巴可用来存储脂肪<ref>{{cite web|url=http://animal.discovery.com/mammals/platypus/ |title=Platypus : Facts, Pictures : Animal Planet |publisher=Animal.discovery.com |date=16 November 2011 |accessdate=8 September 2012}}</ref>。約4個月哺乳期後獨立生活，2歲半為成年。

=== 毒液 ===

雌性和雄性鸭嘴兽的踝部都有尖刺，只有雄性的可以从踝部腺体分泌毒液、由毒刺排出以自卫<ref>{{cite web |url=http://www.australianfauna.com/platypus.php |title=Australian Fauna |publisher=Australian Fauna |accessdate=14 May 2010 |deadurl=yes |archiveurl=https://web.archive.org/web/20120529040439/http://www.australianfauna.com/platypus.php |archivedate=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 |accessdate=14 May 2010}}</ref><ref>{{cite web |url=http://rainforest-australia.com/platypus_poison.htm |title=Platypus poison |publisher=Rainforest Australia |accessdate=14 May 2010 |deadurl=yes |archiveurl=https://web.archive.org/web/20100529165453/http://rainforest-australia.com/platypus_poison.htm |archivedate=29 May 2010 }}</ref><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| accessdate = 14 September 2006}}</ref>。其毒素对小型动物如狗等来说是致命的。虽然对人类来并非如此，但仍然会造成剧烈疼痛使人丧失行动能力<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''.</ref>。被其扎伤之后，伤处先是迅速产生水肿，然后扩散到其他部位。治愈之后仍然会导致患者[[痛觉过敏]]达数日乃至数月之久<ref name="JN">{{cite journal|journal= Journal of Neurophysiology|title=Venom From the Platypus, ''Ornithorhynchus anatinus'', Induces a Calcium-Dependent Current in Cultured Dorsal Root Ganglion Cells |author=de Plater, G.M.|author2= Milburn, P.J.|author3= Martin, R.L.|volume=85|issue=3|pages=1340–5|year=2001 |url=http://jn.physiology.org/cgi/reprint/85/3/1340|pmid= 11248005}}</ref><ref name="venom">{{cite web|url=http://www.kingsnake.com/toxinology/old/mammals/platypus.html |title=The venom of the platypus (''Ornithorhynchus anatinus'') |accessdate=13 September 2006 |deadurl=yes |archiveurl=https://web.archive.org/web/20120201185504/http://www.kingsnake.com/toxinology/old/mammals/platypus.html |archivedate=1 February 2012 }}</ref>。

雌兽有两个卵巢，但只有左卵巢有用<ref name="EC" />。一次最多产三枚卵（通常为两枚），卵略呈椭圆形，直径11公釐（0.43英寸）<ref name="BSED">{{cite journal|journal= Philosophical Transactions of the Royal Society B: Biological Sciences|title=Early development and embryology of the platypus|author=Hughes, R. L. |author2=Hall, L. S. |volume=353|issue=1372|pages=1101–14|publisher=The Royal Society|date=28 July 1998|pmid= 9720108|pmc= 1692305 | doi = 10.1098/rstb.1998.0269}}</ref>。卵在卵巢内待28天，孵化只需要10天。<ref name="RS2">{{cite journal|journal=Philosophical Transactions: Biological Sciences|title =The development of the external features of the platypus (''Ornithorhynchus anatinus'')|author=Manger, Paul R. |author2=Hall, Leslie S. |author3=Pettigrew, John D. |volume=353|issue=1372|pages=1115–25|date=29 July 1998|pmid=9720109|publisher=The Royal Society|pmc=1692310|doi =10.1098/rstb.1998.0270}}</ref>

刚出生的鸭嘴兽眼睛看不见东西，仅靠母乳为生。鸭嘴兽虽然有[[乳腺]]，但是没有乳头，其母乳是通过皮肤上的毛孔流出的，小鸭嘴兽会舔食积聚在母兽腹部的乳汁<ref name="APC" /><ref name="EPA" />。哺乳期为三至四个月。孵化期和哺乳期间，母兽会短暂外出觅食，离开前用土块挡住巢穴入口以保护幼兽<ref name="QM">{{cite web|url=http://www.qm.qld.gov.au/inquiry/factsheets/leaflet0010.pdf|title=Egg-laying mammals|publisher=Queensland Museum|date=November 2000| accessdate = 19 June 2009|format=PDF|archiveurl = https://web.archive.org/web/20080722180447/http://www.qm.qld.gov.au/inquiry/factsheets/leaflet0010.pdf |archivedate = 22 July 2008|deadurl=yes}}</ref>。哺乳期过后幼兽才会外出<ref name="EPA" />。

==演化過程==

最古老的鴨嘴獸的[[化石]]發現於10萬年前的[[第四紀]]地層。一些科學家認為''[[Teinolophos]]''、''[[Steropodon]]''是鴨嘴獸的祖先<ref name="Thomas H. Rich 2016">Thomas H. Rich, James A. Hopson, Pamela G. Gill, Peter Trusler, Sally Rogers-Davidson, Steve Morton, Richard L. Cifelli, David Pickering, Lesley Kool, Karen Siu, Flame A. Burgmann, Tim Senden, Alistair R. Evans, Barbara E. Wagstaff, Doris Seegets-Villiers, Ian J. Corfe, Timothy F. Flannery, Ken Walker, Anne M. Musser, Michael Archer, Rebecca Pian and Patricia Vickers-Rich (2016). "The mandible and dentition of the Early Cretaceous monotreme Teinolophos trusleri". Alcheringa: An Australasian Journal of Palaeontology. in press. doi:10.1080/03115518.2016.1180034.</ref>，但是實際上其演化是相對獨立的<ref name="MS">{{cite journal|journal=Acta Palaeontologica Polonica |url=http://www.app.pan.pl/archive/published/app47/app47-487.pdf|format=PDF|title=New data on the Paleocene monotreme ''Monotrematum sudamericanum'', and the convergent evolution of triangulate molars|author=Pascual, R.|author2= Goin, F.J.|author3= Balarino, L.|author4= Udrizar Sauthier, D.E.|volume=47|issue=3|pages=487–492|year=2002}}</ref>。

2004年[[澳大利亞國立大學]]的研究人員發現鴨嘴獸擁有十條[[性染色體]]（大多數哺乳動物只有XY兩條）<ref name="discover">{{cite web|url=http://discovermagazine.com/2005/apr/sex-ys-platypuses0425/|title=Sex, Ys, and Platypuses|publisher=Discover|first=Jocelyn|last=Selim|date=25 April 2005| accessdate = 7 May 2008}}</ref>。與鳥類<ref>{{Cite journal