Gait diagram in quadruped locomotion obtained from behavioural observations of animals. Highlighted regions represent the stance phase. (a) A zebra's lateral-sequence (L-S) walk (see electronic supplementary material, movie S1), in which the feet touch down in the order right hind (RH), right fore (RF), left hind (LH) and left fore (LF). (b) A Japanese monkey's diagonal-sequence (D-S) walk (see electronic supplementary material, movie S2), in which the feet touch down in the order RH, LF, LH and RF. These photographs are frames from videos (see electronic supplementary material, movies S1 and S2) recorded at Yagiyama Zoological Park. Captive animals housed in the zoo were videotaped using a CASIO EX-F1 at 600 frames per second as they walked on flat ground.