| Summary: | Among the different models that have been proposed to explain the origin of avian flight<br />from terrestrial predators, the cursorial and arboreal hypotheses remain the most discussed.<br />However, the fossil data at hand show that, taken separately, both theories have significant<br />limitations in explaining the origin of flight in bird lineage. Here, we describe an aerodynamics<br />principle that fills in the gaps between those apparently contradictory models. The upslope wind in<br />mountain areas and strong wind in plains provided the meteorological conditions allowing<br />feathered paravians to glide. The results suggest that smaller, feathered paravians could be lifted to<br />glide down to trees on mountain slopes or even to glide up to high trees in plain areas when meeting<br />a strong airflow as they were pursuing a prey or escaping from a predator. The development of<br />more aerodynamical limb feathers was a key factor for gliding down the trees because of the<br />dependency of the resultant force on the surface area of a paravian’s body. Later in the evolution<br />process, paravians learned to change the orientation of their wings to gain higher lifts. The proposed<br />principle and the results obtained in the present research help to better estimate the aerodynamic<br />behavior of extinct species and will also help to design an efficient and beneficial system for future<br />flying robots.
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