Possible adaptive significance of the open pelvis of birds and a new hypothesis of the origin of flight. - S.A. Loparev. - Berkut. 5 (2). 1996. P. 216-230.
There are three hypotheses of the origin of avian pelvis. All of them have some weak points. We propose a hypothesis on the origin of backward orientation of pubis intended for containing a big postembryonic yolk mass. This structure exists in overwhelming majority of recent species and corresponds with relatively big (when compare with adult birds) dimensions of new born nestlings as well as with short term and high rate of their development. Existing hypotheses on the origin of flight underrate the energetics of take-off flight. We suppose that the origin of flight lies in the following row of events. 1) In coastal or littoral habitats some forms use to escape from danger by flapping the "protowings" on water. Normally these "protowings" are used for quite different purpose. 2) On the base of such behavior a gliding flight originates. Legs and wings are used in succession as propelling agents. 3) Subsequently "a flight above the screen" is formed. This type of flight requires less energy and permits transportation on a long distance. 4) Only after all of these stages forward horizontal flight is formed. All other types of flight originate later within bird species adapted to different habitats and possessed substantial reserve of power for rapid take-off flight and for change of flight regimes. We propose a system of characters of class Aves in the process of formation. In addition to generally accepted avian features it includes: relatively small dimensions, small number of eggs in a single clutch, asynchronous development and successive laid of eggs, the most rapid within tetrapodes rate of growth and short term of development. There is a rather rigid system of links among the majority of these characters which promotes improvement of flight and complication of behaviour. [Russian].
Key words: morphology, evolution, pelvis, development, flight.