Assessing Arboreal Adaptations of Bird Antecedents: Testing the Ecological Setting of the Origin of the Avian Flight Stroke

The origin of avian flight is a classic macroevolutionary transition with research spanning over a century. Two competing models explaining this locomotory transition have been discussed for decades: ground up versus trees down. Although it is impossible to directly test either of these theories, it is possible to test one of the requirements for the trees-down model, that of an arboreal paravian. We test for arboreality in non-avian theropods and early birds with comparisons to extant avian, mammalian, and reptilian scansors and climbers using a comprehensive set of morphological characters. Non-avian theropods, including the small, feathered deinonychosaurs, and Archaeopteryx, consistently and significantly cluster with fully terrestrial extant mammals and ground-based birds, such as ratites. Basal birds, more advanced than Archaeopteryx, cluster with extant perching ground-foraging birds. Evolutionary trends immediately prior to the origin of birds indicate skeletal adaptations opposite that expected for arboreal climbers. Results reject an arboreal capacity for the avian stem lineage, thus lending no support for the trees-down model. Support for a fully terrestrial ecology and origin of the avian flight stroke has broad implications for the origin of powered flight for this clade. A terrestrial origin for the avian flight stroke challenges the need for an intermediate gliding phase, presents the best resolved series of the evolution of vertebrate powered flight, and may differ fundamentally from the origin of bat and pterosaur flight, whose antecedents have been postulated to have been arboreal and gliding

A numerical exploration of parameter dependence in power optimal flapping flight

A computational framework for analyzing and designing efficient flapping flight vehicles is presented. Two computational tools are considered: a Betz Criterion code proposed by Hall et. al., and an accelerated, unsteady, potential flow solver. The parameters considered in this paper are: the flapping frequency, the flapping amplitude in both up-down and forward-aft directions, and the addition of a mid-wing hinge for articulated flapping flight. The flapping kinematics are represented using harmonics. Three numerical experiments are examined for the flapping flight analysis. The first experiment involves sweeping through a basic flapping flight parametric design space. The second experiment minimizes flight power at a given flight condition using a quasi-Newton optimization. The third experiment demonstrates the conversion of the problem from a wake only analysis to a 3-D flapping wing geometry. Φ up-down flapping angle Ψ fore-aft (sweep) angle φ phase lag in Φ ψ phase lag in Ψ b span c chord s arc length along wing sj arc length position of joint t time XY Z Cartesian location in space uvw Cartesian velocity components U wing center-point velocity (in −X direction) V total local velocity ω primary flapping frequency ¯sj fractional joint position ( = 2sj/b) µ advance ratio ( = U/(ωb) Γ wing circulation cℓ section lift coefficient ( = 2Γ/cV) cd section drag coefficient constant coefficient of profile-drag polar cd