Shifts in stability and control effectiveness during evolution of Paraves support aerial maneuvering hypotheses for flight origin

Abstract

The capacity for aerial maneuvering was likely a major influence on the evolution of flying animals. Here we evaluate consequences of paravian morphology for aerial performance by quantifying static stability and control effectiveness of physical models for numerous taxa sampled from within the lineage leading to birds (Paraves). Results of aerodynamic testing are mapped phylogenetically to examine how maneuvering characteristics correspond to tail shortening, forewing elaboration, and other morphological features. In the evolution of Paraves we observe shifts from static stability to inherently unstable aerial planforms; control effectiveness also migrated from tails to the forewings. These shifts suggest that some degree of aerodynamic control and and capacity for maneuvering preceded the evolution of strong power stroke. The timing of shifts also suggests features normally considered in light of development of a power stroke may play important roles in control.

Evolution of avian flight: muscles and constraints on performance

“…Invoking St cruise in relation to historical transformations leads to the conclusion that an evolutionary trajectory must have been from low-amplitude, low-frequency wing movement when an animal is moving slowly towards higher-amplitude, higherfrequency flapping when moving faster [53]. Thus, this analysis is consistent with the predictions of the incremental changes in the trajectory of wing kinematics in the directed aerial descent hypothesis [46,50]. There are two potential shortcomings of invoking St cruise as a model for flapping motion during slow-speed locomotion, however.…”

“…In direct competition with this idea, recent research into the gliding and steering capacity of insects and other non-avian taxa including amphibians [45][46][47] leads to a 'directed aerial descent' hypothesis in which static stability associated with wing and tail postures in parachuting and gliding [48,49] requires less from the neuromuscular and skeletal system, and therefore reveals that gliding is more parsimonious as the ancestral precursor to bird flight [50].…”

“…Different fossil evidence is invoked to support the fundamental wing-stroke hypothesis [32] or the directed aerial descent hypothesis [5,46,50]. Analysed in the context of a flapping origin, the locomotor capacity of fossil forms has been bracketed or estimated using fossilized details of wing anatomy and body size, extant data on limb kinematics in flying birds and running lizards, and empirical measures of aerodynamic force production by the partially developed wings of juvenile birds [51].…”

“…Clearly, though, caution is warranted as the musculoskeletal system of modern birds is highly derived compared with their ancestors. In support of directed aerial descent, incremental improvements in the capacity for stability and manoeuvring are apparent when minor postural changes are made during gliding as measured in physical models designed upon the anatomy of a fossilized four-winged theropod [50]. A possible explanation for the lack of extant intermediate styles of wing motion is that they may not represent peaks in an adaptive landscape sensu Wright [52].…”

“…A possible explanation for the lack of extant intermediate styles of wing motion is that they may not represent peaks in an adaptive landscape sensu Wright [52]. This possibility merits testing in ways that integrate palaeontology, phylogenetics and biomechanics [32,50,51]. Figure 1.…”