A NEW THEORY OF THE ORIGIN OF BIRD FLIGHT
SUMMARY
Data from video clips present frame-by-frame slow motion evidence which shows that in the immediate takeoff by eagles and herons there are simultaneous wing-and-leg rotations, and so give evidence to the presence of a built-in co-rotational coordination of front and hind limb actions.
4. ADDITIONAL MATERIALS INCLUDE:
This action is, of course, what all previous cursorial-based theories have recognized and utilized (though only in connection with running, jumping, and most recently with vertical plane running (WAIR). Nevertheless, a truly convincing, unbroken chronology of flight evolvement could not be laid out because the search entered a cul-de-sac.
There are two reasons for this failure: (a) looking for a secondary arm flap movement to assist primary leg action in locomotion and (b) looking for an answer in locomotory action.
Removal of these two allow consideration of a hind-leg action which is not locomotive but is relatively stationary, namely: striking with the hind-claw, a behavior ubiquitous in avian aggression and one of high fitness selective value.
As categorically shown by data and analysis in this manuscript, unified arm-leg coaction is a physiologically built-in mechanism in (relevant) vertebrates, and demonstratively, even in humans, and therefore locomotion is not necessary to generate simultaneous action of forelimbs and hind limbs. The sizable video and photographic data offered clearly illustrates that striking with hind claws is in all instances accompanied by rapid and powerful wing flaps. (We may confidently challenge anyone to show cases where this is not true). The manuscript offers (on CD) slow-motion analysis of these actions that most definitely enables seeing what normally is too rapid to observe. Seeing this action, it is hard to imagine how such commonly found behavior could have been missed.
An entirely new, never described systematization of built-in vertebrate limb coordination, detailed through a full survey and systematization of coordinated limb action in all five vertebrate classes and their subdivisions. An analysis that explains how WAIR is an automatic CR arm-leg coaction. The physical mechanics of the flight stroke, and its presence in humans. A discussion of the Glide theories of bird flight which brings to light a so-far not recognized major error in their argument involving thermoregulation. This section is based on a detailed survey of all gliding animals.
Thus, if small bidepal, running carnivorous dinosaurs utilized (and even have, as it is so well documented, specialized in) hind-claw aggression, and if both flying and flightless birds nearly universally engage in this behavior, then lift, without running or jumping was potentially present in the protobird, and only required the appearance of feathered flight surfaces on the arms. A concise evolution and chronology of flight origins can thus be described. Above all, this theory is uniformitarian: the source of flight is observable in current bird behavior.
