I recently came across a couple of very cool papers about animal locomotion: Collins and Stewart, "Symmetry-breaking bifurcation: A possible mechanism for 2:1 frequency-locking in animal locomotion," J. Math. Biol. (1992) 30:827-838 Collins and Stewart, "Coupled Nonlinear Oscillators and the Symmetries of Animal Gaits," J. Nonlinear Sci. Vol. 3: pp. 349-392 (1993) PDFs can be found by googling. On p. 34 of the second one is a nifty example that I thought would be of interest to students in the kind of survey course that biology majors have to take. As a salamander crawls, its body wiggles in a standing-wave pattern. A dogfish makes a traveling wave. I thought the salamander example was cool enough that I created a drawing for my online textbook http://www.lightandmatter.com/lm/ (section 20.4).