What is Spur (zoology)?
[[File:Spur-Winged-Plover444.jpg|thumb|right|[[Wing]] spurs on a [[Masked lapwing]] in [[flight]]]] A '''spur''' is a [[bone]] covered in [[keratin|horn]] that grows out of an [[animal|animal's]] body. While [[claw]]s or [[Nail (anatomy)|nails]] grow from the [[toe]]s, spurs grow on other parts of the [[foot]]. These parts are usually connected with [[joint]]s.<ref>{{cite journal|last=Fisher|first=H.I.|title=The occurrence of vestigial claws on the wings of birds|url=https://archive.org/details/sim_american-midland-naturalist_1940-01_23_1/page/234|journal=American Midland Naturalist|year=1940|volume=23|issue=1|pages=234–243|jstor=2485270|doi=10.2307/2485270}}</ref> Spurs are mostly found on the hindfeet, but some birds have spurs at the edge of their wings.<ref name=Rand>{{cite journal|last=Rand|first=A.L.|title=On the Spurs on Birds' Wings|journal=The Willson Bulletin|year=1954|volume=66|issue=2|pages=127–134|url=http://sora.unm.edu/sites/default/files/journals/wilson/v066n02/p0127-p0134.pdf|accessdate=16 November 2012}}</ref> ==In mammals== [[File:Platypus spur.JPG|right|thumb|The [[calcaneus]] spur on the [[male]] [[platypus]]' hind limb is [[venom]]ous.]] Not many mammals have spurs. The male [[platypus]] has spurs on the heels of its hind feet. The spurs are [[wikt:hollow|hollow]] and [[wikt:connect|connected]] to a venom [[gland]]. This helps the platypus kick [[wikt:painful|painfully]].<ref>{{cite web |url=http://www.australianfauna.com/platypus.php |title=Australian Fauna |publisher=Australian Fauna |accessdate=2010-05-14 |archive-date=2016-03-04 |archive-url=https://web.archive.org/web/20160304125122/http://australianfauna.com/platypus.php |url-status=dead }}</ref> [[Echidna]]s have spurs as well, but they are not venomous.<ref>{{cite book|last=Griffiths|first=Mervyn|title=The biology of the monotremes|url=https://archive.org/details/biologyofmonotre0000grif|year=1978|publisher=Academic Press|location=New York|isbn=0123038502}}</ref> [[Fossil]]s of some early mammals are found to have spurs also.<ref>{{