Fig. 5. Phylogeny of dinosaurs (Gauthier, 1986; Sereno, 1999; Holtz, 2000) showing the distribution of characters that are likely to have decreased rotational inertia. 1, pubes retroverted; 2, S-shaped neck; 3, cervical vertebrae pneumatized; 4, dorsal vertebrae pneumatized; 5, manus tridactyl; 6, forelimb reduced; 7, tail shortened; 8, manus didactyl; 9, head size reduced; 10, teeth lost; 11, body size reduced; 12, tail reduced, but more robust proximally. The functional significance of the characters is discussed in the text.