Fig. 9: Evolution and scaling of relative head, neck and torso size in herbivorous tetrapods.

Results for the OUwie analysis for head to neck ratio evolution with respect to dietary ecology, showing estimates of A macroevolutionary optimum (θ), B selection strength (ɑ) and C evolutionary rate (Hypothesis 3). In all three panels, each point corresponds to the parameter estimate for one of the sampled simulated evolutionary regimes. Consistent with Hypothesis 8, carnivores have greater D head sizes relative to body size and A, G relative to neck size compared to herbivores and other trophic groups. Contra to Hypothesis 8, E neck size relative to body size appears to be similar between carnivores and herbivores. The tendency towards larger heads and smaller necks in carnivores compared to herbivores (particularly at larger body sizes) is reflected in evolutionary transitions between these dietary ecologies in H mammals, I dinosaurs and J birds. F Carnivores and herbivores have larger torso volumes relative to limb lengths than other trophic groups, but do not differ from each other. Circled numbers in H represent: 1= Pecora; 2 = Suina; 3 = Arctoidea; 4 = Canidae; 5 = Felidae). Circled numbers in I represent: 1 = Sauropoda; 2 = Neosauropoda; 3 = Titanasauriformes; 4 = Theropoda; 5 = Eumaniraptora). Circled numbers in (J) represent: 1= Aves; 2 = Palaeognathae; 3= Galliformes; 4 = Aequorlitornithes; 5 = Aequornithes; 6 = Accipitriformes; 7 = Afroaves; 8 = Australaves). WBCHV, whole-body convex hull volume. Source data are provided as a Source Data file. Animal images created with BioRender.com.