Gregory, W. K., 1912, Notes on the principles of quadrupedal locomotion and the mechanisms of the limbs in hoofed animals: Annals of the New York Academy of Sciences, v. 22, p. 267-292.

Sloan, R. E. et al., 1986, Gradual dinosaur extinction and simultaneous ungulate radiation in the Hell Creek Formation: Science, v. 232, p. 629-633.

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