THE METABOLIC STATUS OF SOME LATE CRETACEOUS DINOSAURS

Analysis of the nasal region in fossils of three theropod dinosaurs (N anotyrannus, Ornithomimus, and Dromaeosaurus) and one ornithischian di nosaur (Hypacrosaurus) showed that their metabolic rates were signific antly lower than metabolic rates in modern birds and mammals. In extan t endotherms and ectotherms, the cross-sectional area of the nasal pas sage scales approximately with increasing body mass M at M(0.72). Howe ver, the cross-sectional area of nasal passages in endotherms is appro ximately four times that of ectotherms. The dinosaurs studied here hav e narrow nasal passages that are consistent with low lung ventilation rates and the absence of respiratory turbinates.