Aerodynamics from Cursorial Running to Aerial Gliding for Avian Flight Evolution

Among the different models that have been proposed to explain the origin of avian flightfrom terrestrial predators, the cursorial and arboreal hypotheses remain the most discussed.However, the fossil data at hand show that, taken separately, both theories have significantlimitations in explaining the origin of flight in bird lineage. Here, we describe an aerodynamicsprinciple that fills in the gaps between those apparently contradictory models. The upslope wind inmountain areas and strong wind in plains provided the meteorological conditions allowingfeathered paravians to glide. The results suggest that smaller, feathered paravians could be lifted toglide down to trees on mountain slopes or even to glide up to high trees in plain areas when meetinga strong airflow as they were pursuing a prey or escaping from a predator. The development ofmore aerodynamical limb feathers was a key factor for gliding down the trees because of thedependency of the resultant force on the surface area of a paravian’s body. Later in the evolutionprocess, paravians learned to change the orientation of their wings to gain higher lifts. The proposedprinciple and the results obtained in the present research help to better estimate the aerodynamicbehavior of extinct species and will also help to design an efficient and beneficial system for futureflying robots