Editing Echidna (section)

==Anatomy==
Echidnas and platypuses are the only egg-laying mammals, the [[monotremes]].
The average lifespan of an echidna in the wild is estimated at 14–16 years. Fully grown females can weigh about {{convert|4.5|kg}}, the males 33% larger, at about {{convert|6|kg}}.<ref name="NSW"/> Though the internal reproductive organs differ, both sexes possess an identical single [[cloaca]] opening for urination, defecation, and mating.<ref name=CSIRO06/>

Male echidnas have non-venomous [[spur (zoology)|spurs]] on the hind feet, similar to the venomous male platypus.<ref>{{cite book|last=Griffiths|first=Mervyn|title=The biology of the monotremes|year=1978|publisher=Academic Press|location=New York|isbn=0123038502}}</ref>

Due to their low [[metabolism]] and accompanying stress resistance, echidnas are long-lived for their size; the longest recorded lifespan for a captive echidna is 50 years, with anecdotal accounts of wild individuals reaching 45 years.<ref name=andiv09/> 

The echidna's brain is half [[neocortex]],<ref name="bbc121119" /> compared to 80% of a human brain.<ref name="Dunbar1993">{{cite journal |author=Dunbar, R.I.M. |year=1993 |title=Coevolution of neocortical size, group size and language in humans |journal=Behavioral and Brain Sciences |volume=16 |issue=4 |pages=681–735 |doi=10.1017/S0140525X00032325 |s2cid=145583615}}</ref><ref name="Dunbar1998">{{cite web |last=Dunbar |first=R.I.M. |title=The Social Brain Hypothesis |url=http://psych.colorado.edu/~tito/sp03/7536/Dunbar_1998.pdf |url-status=dead |archive-url=https://web.archive.org/web/20160412210459/http://psych.colorado.edu/~tito/sp03/7536/Dunbar_1998.pdf |archive-date=12 April 2016 |access-date=4 January 2014 |website=University of Colorado at Boulder, Department of Psychology and Neuroscience}}</ref> Contrary to previous research, the echidna does enter [[Rapid eye movement (sleep)|REM]] sleep, but only in a comfortable temperature around 25&nbsp;°C (77&nbsp;°F). At lower or higher temperatures of 15&nbsp;°C (59&nbsp;°F) and 28&nbsp;°C (82&nbsp;°F), REM sleep is suppressed.<ref name="nsl0003" />