What is Bird feet?
[[File:Bird-feets.png|thumb|200px|right|Types of bird feet]] [[File:Bird leg and pelvic girdle skeleton EN.gif|thumb|upright=1.35|Bird left leg and [[pelvic girdle]] skeleton]] '''Bird feet''' are [[adapted]] to the life they lead, and the patterns are often use in avian classification. They are derived from the basic [[limb]] of [[basal|ancestral]] [[tetrapods]], the [[pentadactyl limb]]. Humans (and other [[primates]]) have the original five fingers and five toes. Most birds have four toes, inherited together with over a hundred anatomical features from their [[theropod]] dinosaur ancestors.<ref>Mayr, Gerald 2016. ''Avian evolution''. Wiley. doi:10.1002/9781119020677. ISBN 9781119020677.</ref> These four toes are arranged into four main patterns.<ref name=Proctor&Lynch>Proctor N.S. & Lynch P.J. 1998. ''Manual of Ornithology: avian structure & function''. Yale University Press. {{ISBN|0300076193}}</ref> == Arrangement of toes == #'''Anisodactyly'''. This is the most common arrangement of toes in birds, with three toes forward and one back. It is the basic pattern in [[passerine]] birds, especially the [[songbirds]], and hunting birds like [[eagle]]s, [[hawk]]s, and [[falcon]]s. <br/>The anisodactyl arrangement lets passerine birds perch on vertical surfaces, such as trees and cliffs. The hind toe joins the leg at the same level as the front toes. <br/>The leg arrangement of passerine birds has a special adaption for perching: a ''tendon-locking mechanism''. A [[tendon]] in the rear of the leg is automatically pulled and tightened when the leg bends. This makes the foot curl stiffly round when the when the bird lands on a branch. The tendon is locked in place by another tendon. So passerines sleep while perching without falling off.<ref>Stefoff, Rebecca 2008. ''The bird class''. Marshall Cavendish Benchmark.</ref><ref>Brooke, Michael and Tim Birkhead 1991. ''The Cambridge Encyclopedia of Ornitholigy''. Cambridge University Press.</ref> <br/>Certain species of passerines have stiff tail feathers, which help the