BREATHING LIFE BACK INTO DINOSAURS: COMPUTER MODELING OF NASAL AIRFLOW IN DINOSAURS AND THEIR EXTANT RELATIVES

Respiratory turbinates (RTs), the mucosal scrolls that line the airways of extant birds and mammals, are believed to play a critical role in retaining internal heat and moisture. The near cosmopolitan distribution of RTs in birds and mammals has led some to suggest that the presence of RTs in extinct animals like dinosaurs is necessary and sufficient to infer endothermy. Previous studies have looked for RTs in dinosaurs, but the overall conformation of the nasal passage itself has remained unexplored. The internal architecture of this cavity is critical for any study of the effects of RTs in respiratory physiology. A computational fluid dynamics (CFD) analysis was performed on an extant outgroup to dinosaurs (Crocodylia). The digital nature of CFD allows for morphological manipulations that would be untenable for live animals (e.g., adding, removing, or relocating RTs in the nasal passage). A 3D model of the airway of Alligator mississippiensis was created from CT data and input into the CFD program Fluent (ANSYS). Results showed the dorsoventrally compressed rostral third of the nasal passage forming laminar flowing air during relaxed respiration. More complex, slower moving air was seen looping around the olfactory region. Areas of laminar airflow combined with other work on vasculature indicate the possibility of a counter-current flow system that may function in a way analogous to the RTs found in birds and mammals. These results suggest that alternative approaches to conditioning respired air may exist. Future work on ostriches will compare airflow in nasal passages with RTs and after their (digital) removal. These data will allow for airflow reconstruction in a number of dinosaur taxa. Only by understanding how air is affected by nasal anatomy in extant taxa can we begin to infer with any confidence the flow of air in dinosaurs, and what this reconstructed airflow might say about dinosaur physiology. Preliminary CFD work on an airway model from the Cretaceous theropod dinosaur Majungasaurus crenatissimus revealed a similar pattern to the alligator with the airway proper showing laminar flow while slower moving air in the much enlarged olfactory region was more turbulent. Simulations in Majungasaurus of nasal airflow with modeled RTs reveal the impact of RTs on flow dynamics and consequently nasal physiology.