newtheory

3. The new theory about the origin of flight (published in 1996)

For a long time it was assumed that the ability to fly could only have evolved in the air. Moreover, it was assumed that a ‘primordial’ wing was already present which made flying soon possible. These assumptions are not in agreement with Darwin’s ideas. I have abandoned these presumptions completely, since they were not at all compelling. This change in looking at problems opened my eyes and made a new explanation easily possible. The transition from arms to wings presented the main problem so far. A convin- cing idea must in any case be able to explain the formation of the wing, emanating from an unspecialized arm and assuming a conti- nuous process which does not erect fences too big for any transitional form. Obviously, this transition was not possible in the air. But for the evolution of the wing beat the involved complicated movement had to be developed already in early as well in transitional forms, however, not necessarily in the air. The wing beat is not simply a flapping movement of arms and hands up and down, as it may look at first view, but it includes a complicated superimposed rotational motion.

Former ideas about the evolution of flight suffered from the handicap that they were unable to explain the origin of the wing and the evolution of the wing beat. As mentioned above, Darwin was fully aware of this problem, and he presumed a modification of a former function, but he did not find such a function. Certainly, his presumption was correct, but his modern adherents apparently did not understand his reservations. Ideas offered so far are simply too amateurish. Unfortunately, these models demonstrate the missing ability of palaeontologists to propagate really new ideas. The reason for this deficiency is probably caused by their education which does not yield methods for an unequivocal judgement of new ideas as to plausibility and compatibility with physical laws, thus lea- ding to a deep uncertainty. Sometimes this uncertainty is compensated by self-confidence and even by arrogance. As a consequen- ce incorrect ideas persist to be claimed. Those old and new self-made experts cannot have been incorrect, let us go on to spin yarns! Did these people forget their brains when leaving universities? For example:

Jeremias M. V. Reyner: On the origin and evolution of flapping flight aerodynamics in birds, 363-385 in Jacques Gauthier & Lawrence F. Gall (eds): New Perspectives on the Origin and Early Evolution of Birds: Proceedings of the International Symposium in Honor of John H. Ostrom, Yale Peabody Museum 2001.

"Alternative paradigms for flight evolution“

Debate about avian flight evolution has rarely extricated itself from the polarized cursorial or arboreal models, or from compromise hypotheses of the type raised here. An alternative biomechanical model for the origin of flight has been put forward recently by Ebel (1996); this is similar to a hypothesis I advanced -- in part in jest -- somewhile before (Reyner 1985d).

Does he claim priority? This idea, that flight evolved underwater, is consistent with the taphonomy of Archaeopteryx in the shallow lagoonal environment of Solnhofen, and also with speculation of a piscivorous diet. It is also an attractive idea for mechanical reasons, since the density of water is sufficiently high to support most of an animal's weight by buoyancy. Several other lineages of tetrapods that have secondarily become obligate swimmers have evolved similar swimming mechanisms using the forelimbs as wings, and effectively flying underwater (ichthyosaurs, plesiosaurs, marine turtles, sea lions). This adaptation is a particularly effective form of locomotion, and all of these groups are particularly efficient swimmers. It has also evolved independently in several avian groups; some have become secondarily flightless (penguins, some ducks and some alcids), while others can fly in both water and air (some ducks, diving petrels, morid gannets, some alcids, and dippers). Evidently this swimming mode presents rather few mechanical or morphological obstacles. Unfortunately, this model cannot explain avian evolution, and the evidence against it comes from the morphology of Archaeopteryx. All wing propelled underwater fliers among birds have unusually large supracoracoideus muscles to elevate the wing during the upstroke (Reyner 1988b). Yet Archaeopteryx had no supracoracoideus (Ostrom 1976b; see above), and there is no evidence of another wing elevator muscle. Although insubstantial, this brief digression is informative. The origin of flight may have followed a pathway appreciably distant from those normally envisaged, or discussed here. Both cursorial and arboreal models, as normally formulated, raise significant difficulties that have yet to be resolved. A combination of unusual, or possibly rapidly changing, environmental conditions may be responsible, and this may make such hypotheses resistant to physical modeling of the kinds reviewed here."

Bad luck, thus, a deus ex machina must be postulated and will certainly help to resolve all problems. Unfortunately, this is basically the usual simple argumentation of these ”experts”, who cannot produce correct ideas, and even cannot judge plausible ones. But they claim to be experts, without the slightest reservations.

Flying under water creates the pre-conditions to flying in the air

Archaeopteryx has already wing bones looking almost as those of modern birds. However, in detail there are differences. There must be a certain reason for these differences. I am deeply convinced that they result from the fact that Archaeopteryx was primarily an underwater flyer, not capable of flying in the air. Many water-dwelling vertebrates such as turtles for example use almost the same course of wing motion as birds do. Moreover, reptiles older than Archaeopteryx had developed a sternum which is believed to be lost later on, although this presumption is not beyond doubt. Indeed, water-dwelling reptiles with so-called rowing arms were widespread during the Triassic period. Apparently, there was a considerable selective pressure towards a modification of the anterior extremities as propulsive organs. Presumably the proceeding radiation of fish offered a new very attractive food source.

Fig. 10. Comparison between the arm bones of Archaeopteryx and a modern bird

Having seen a TV-documentation showing an auk in pursuit of a fish under water the idea struck me that birds as descendants of reptiles might as well have learned flying under water and extended this capability later on to the air. I have critically reflected about this possibility and have not found any arguments contradicting this idea, only confirmations. There are, on the other hand, many advantages supporting such a development, with the evolution of flight in the air only being a kind of by-product which did not happen as an original evolutionary aim. Presumably, there is no directed evolution at all, although after- wards such an impression may arise. Evolution is a continuous sequence of chances that can be interrupted by unfavourable circumstances at any point of the process.

In my opinion the evolution began in a necessarily small theropod which used its arms and hands as propulsive organs for hunting fish under water, as many close or remote relatives such as ichthyosaurs, plesiosaurs, turtles, rhamphorhynchoids etc. did. This idea demonstrates a continuous path to the ability to fly in the air, since

there was no hazard of crash, because under water the animal was carried by its buoyancy,
the flight musculature could improve simultaneously with increasing wing span and wing area,
the most favourable movement for the generation of propulsion could develop step by step,
only propulsion, but no lift was required,
the motion was active only for a short time during pursuit of prey,
the transition to flying in the air became possible within a rather long time, since the animals had to stay near the water surface in the beginning and, therefore, did not fall deep in case of imperfectness.

The evolution of a flying animal can exemplarily be demonstrated in Archaeopteryx and even better in pterosaurs. As you know from your own experience, you can feel well the motion in water if you move a hand through it, since water is 800 times denser than air. Moving a hand through the air as fast as you can does not create an unambiguous impression. Thus in the water an animal can much better feel than in the air the appropriate arm movement that leads to the highest speed. It is certainly not a matter of chance that many water-dwelling vertebrates have independently developed modified arms for the generation of propulsion, though obviously utilizing different strategies leading to different shapes.

Fig. 11. Different shapes of arms and hands in swimmers and flyers

But why are the wings in Archaeopteryx much larger than those of ichthyo- saurs for example? The reason is that ichthyosaurs generate propulsion by bending the trunk and need their arm fins only for steering and manoeuvring (See page locomotion). In contrast to swimmers, in Archaeopteryx the hands are strongly enlarged. This fact is very suggestive. Big hands are favourable for fast locomotion under water. Insofar rubber fins used in the feet of human swimmers are not the best technical solution, but unfortunately the muscles of our arms are too weak.

Archaeopteryx had to generate propulsion exclusively with her arms. This task requires efficient muscles which developed step by step. Locomotion in the water is attained by a backward acceleration of an as big as possible mass of water. For this purpose large hands developed. This development is found in Archaeopteryx as well as in pterosaurs which we can regard simultaneously. Pterosaurs were contemporaries living in the same environment as Archaeopteryx near Solnhofen, Bavaria. Pterosaurs can yield interesting details of the evolutionary process, since there were long- and short-tailed forms, whereas Archaeopteryx is the only known feathered form of this period. Precursors as well as descendants are not known. In contrast to Archaeopteryx the wing of pterosaurs is covered by an integument comparable to bats. Apart from this difference there are many conformities with Archaeopteryx. Although Archaeopteryx had already large hands, nevertheless contrary to birds flying in the air a very important feature, the alula,

Fig. 12. Schematical kinematics of the wing folding in birds

was still missing. The alula is very important for bringing to bear an influen- ce on the flow along the wing in the hand area, in particular at high angles of attack. On the other hand, the kinematics for generating propulsion was completely developed. Propulsion is almost automatically produced, becau- se the twisting effect during pronation and supination is ensured by the complicated design. The necessary distortion is given by the appropriate attachment of the musculature to the bones and its tension. Such a perfect design needs a long evolution and cannot suddenly be present as certain workers would have us believe. A rapid development was not at all required, if these theropods were underwater fish hunters. There was no hazard of crash, and the hunting speed could slowly be increased. Not all fishes are fast swimmers, and they can comparatively easily be caught by hunters. In the lagoons around Solnhofen (Bavaria) fish was very abundant, as many remainders demonstrate, in particular the little Leptolepides sprattiformis which is a very common fossil.

Generation of propulsion can well be observed in rays. The movement of the fins is comparable to the wing movement of underwater flyers and also to birds in the air. The principle of locomotion is always the same, namely a backward transport of water which as a reaction effects a forward motion. It is Newton’s good old mechanical law

F = m x b

The generated force equals the product of mass and its acceleration. This force, propulsion in the water respectively propulsion plus lift in the air is attained by an acceleration of the agent’s mass adjacent to the animal’s body. Since water is considerably denser than air lower voumes ofwater had to be moved compared to air. Therefore, the fences for the evolution of propulsion generated by the arms were not too high. In the air an acceleration of the required capacities is remarkably more difficult. I am deeply convinced that a direct evolution of flight in the air was absolutely impossible. This applies also to the origin of flight in bats.

Fig. 13. Wing motion in rays

The bird wing performs almost the same movement as the fins in rays. The best comparison appears to me the hovering flight of a kestrel. This extremely slow flight is performed with the wing at maximum extension, with propulsion and lift generated simultaneously in order to compensate for the headwind and be able to stay above a certain point on the ground. The almost constant wing span during hovering flight is responsible for the unusual flight manifestation. Size and direction of the force generated by the wing can considerably be varied by birds. In addition, birds can also vary the wing area by folding the wings as required. Thus, there is a wide range of possibilities to modify the generated force as to size and direction which in combination leads to a per- fect flight behaviour in modern birds.

Under water propulsion was generated by the entire arms as in rays or other vertebrates utilizing the extremities for propulsion. Flying in the air makes a division of functions necessary, since the arms generate continuously lift, whereas propulsion is produced by the motile hands.

The long and stiffened bony tail was urgently needed for steering under water !

Fig. 14. Wing (manus) motion in flyers and forces of different size generated by the wing

However, during underwater flight the manus of Archaeo- pteryx and rhamphorhynchoids could only generate pro- pulsive forces, but not in addition the comparatively tiny control forces. This was the function of the long bony tail which in contrast to other theropods was remarkably stiffened, surely for this purpose.

During underwater flight the occurring forces must be balanced. The balance between propulsive force and the hydrodynamic drag confines the attainable maximum speed. It is easily understandable that the evolution of underwater flight in any case began in small forms, since the ratio of mass to muscle area available is most favourable in small forms. The weight of Archaeopteryx was 250 grams approximately. Modern birds exceeding a mass of 2 kg are no more capable of a standing takeoff.

Fig. 15. Level flight under water and acting forces in balance

Large birds such as swans need a long takeoff run, and ma- ny large birds such as ostriches cannot fly at all, since they have become too heavy during evolution. Therefore, the evo- lution of flight capability would not have been possible in an animal considerably heavier than Archaeopteryx or in pre- cursors of Rhamphorhynchus in the Upper Trias. Physical constraints would definitely have prevented such an evoluti- on. Apparently, new lines of specialization always have their origin in small forms which are not yet particularly speciali- zed and adapted to a certain food source.

In the course of time the pectoral musculature had to be strengthened to be able to generate the power needed. However, lift was not necessary before Archaeopteryx proceeded to fly in the air and then had to balance her weight. At this stage all preconditions had been created by perfect adaptation to underwater flight.

The transition to air- borne flight

The last step was the transition from the water to the air. The modifications required for this transition were smaller as it would ap- pear at first view. The size of the generated force remained almost unchanged. Whereas during underwater flight the considerable hydrodynamic drag had to be overcome, in the air the aerodynamic drag is much lower because of the lower density, but now in ad- dition lift had to be produced to compensate for the weight. Thus, the main modification consisted in a change of the direction of the propulsive force. Instead of a forward direction the new direction was forward upward.

An aggravating problem arose, however. During flight under water the position of the centre of gravity had not been of great impor- tance, since the directions of all forces passed through this point. But outside the water the lift force had to change its position which now acted in front of the centre of gravity. The forces of lift and weight resulted in a continuous moment that tilted the animal, it was tail-heavy. For a stable flight the centre of gravity must be located infront of the centre of lift, never behind it.

The long bony tail was urgently required during the transition stage from surface-skimming to air-borne flight

This condition made flying high in the air impossible for long-tailed forms. However, long-tailed forms had the opportunity to escape from this problem by skimming with the tail over the water. The additional force due to friction balanced the moment of the lift force.

Fig. 16. Long-tailed forms were obligatory surface-skimmers, unable to fly high in the air

For this reason all long-tailed forms were obligate surface-skimmers. They were unable to fly high above the water in the air. Their flight resembled at best a swan taking off from the water, but a real lift-off was not feasible. Later on, flying high in the air was another evolutionary step with many obvious advantages. It is very remarkable that these modifications occurred almost simultaneously (in a geological sense) during the Upper Jurassic in pterosaurs and only a short time later in birds.

The long bony tail made a real air-borne flight high in the air impossible and therefore had to be shortened

To become real flyers in the air several characteristic skeletal modifications were inevitable. These modifications affected the

proportions of the wing,
length of the bony tail,
length of neck and skull,
connection between skull and neck,
formation of a closed thoracic cage, the so-called notarium, as a consequence of an increased beat frequency with larger dynamic forces occurring,
absolute size,
reduction of teeth.

Fig. 17. Differences as to the main acting forces in ptero- saurs during flight under water respectively in the air

Most modifications aimed at a forward shift of the centre of gravity. These modifications can only be found in pterodacty- lids, but not in Archaeopteryx. She was restricted to surfa- ce-skimming, flying near the water surface, if at all. Only these modifications led to the required flight stability and made possible an effective fight in the air high above the water surface.

Fig. 18. Necessary skeletal modifications which happened in pterosaurs and testify the transition to flying in the air

The recognition of this relationship is not easy and requires a detai- led knowledge in flight physics, which of course cannot be expec- ted in zoologists or palaeontologists. Nevertheless, for a serious propagation of a new theory about the origin of flight this knowledge is indispensible. Otherwise the old stories will be heard again and again. The application of physical laws, on the other hand, yields very satisfactory results. Up to now the required functional pre-con- ditions had not thoroughly been taken into account.

Because of the considerably higher beat frequency in air, at least about 30 times faster, thoracic cage and shoulder girdle had to be strongly strengthened.There is even a transitional form between Rhamphorhynchus and Pterodactylus, namely the little Anurogna- thus ammoni with approximately 30 cm wing span, again a very small form, compared to other forms with commonly 1 m wing span or more. Curiously, so far it has not been noticed that Anurogna- thus is a very important transitional form. Up to a few years ago all pterosaurs were regarded as flyers in the air.

Fig. 19. Anurognathus as a likely transitional form to real flyers.

Particularly funny appears to me that Anurognathus because of certain features of the skull was placed in the long-tailed forms, although its tail is short and the name (tailless beak) stresses this feature. In any case Anurognathus together with Rham- phorhynchus and Pterodactylus forms a fine line of evolution, with three different forms occurring for some time together and only the short-tailed surviving during the Creta- ceous.

It is very curious and hardly believable that the enormous differences between long- tailed and short-tailed pterosaurs so far have never initiated discussions concerning the meaning for the mode of life. Obviously there is always the same problem, that is, that the workers in this field are missing objective criteria and are restricted to the old method of telling fanciful stories.

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