Constraints on the wing morphology of pterosaurs

Animals that fly must be able to do so over a huge range of aerodynamic conditions, determined by weather, wind speed and the nature of their environment. No single parameter can be used to determine-let alone measure-optimum flight performance as it relates to wing shape. Reconstructing the wings of the extinct pterosaurs has therefore proved especially problematic: these Mesozoic flying reptiles had a soft-tissue membranous flight surface that is rarely preserved in the fossil record. Here, we review basic mechanical and aerodynamic constraints that influenced the wing shape of pterosaurs, and, building on this, present a series of theoretical modelling results. These results allow us to predict the most likely wing shapes that could have been employed by these ancient reptiles, and further show that a combination of anterior sweep and a reflexed proximal wing section provides an aerodynamically balanced and efficient theoretical pterosaur wing shape, with clear benefits for their flight stability.     

First record of a pterosaur landing trackway

The terrestrial progression of pterosaurs, the flying reptiles of the Mesozoic Era, has been debated for over two centuries. The recent discovery of quadrupedal pterodactyloid pterosaur tracks from Late Jurassic sediments near Crayssac, France, shows that the hindlimbs moved parasagittally, as in mammals, birds and other dinosaurs, and the hypertrophied forelimbs could make tracks both close to the body wall and far outside it. Their manus tracks are unique in form, position and kinematics, which would be expected because the forelimbs were used for flight. Here, we report the first record of a pterosaur landing track, which differs substantially from typical walking trackways. The individual landed on both hind feet in parallel fashion, dragged its toes slightly as it left the track, landed again almost immediately and placed the hindfeet parallel again, then placed its forelimbs on the ground, took another short step with both hindlimbs and adjusted its forelimbs, and then began to walk off normally. The trackway shows that pterosaurs stalled to land, a reflection of their highly developed capacity for flight control and manoeuverability.     

There is no trade-off between speed and force in a dynamic lever system

Lever systems within a skeleton transmit force with a capacity determined by the mechanical advantage, A. A is the distance from input force to a joint, divided by the distance from the joint to the output force. A lever with a relatively high A in static equilibrium has a great capacity to generate force but moves a load over a small distance. Therefore, the geometry of a skeletal lever presents a trade-off between force and speed under quasi-static conditions. The present study considers skeletal dynamics that do not assume static equilibrium by modelling kicking by a locust leg, which is powered by stored elastic energy. This model predicts that the output force of this lever is proportional to A, but its maximum speed is independent of A. Therefore, no trade-off between force and velocity exists in a lever system with spring-mass dynamics. This demonstrates that the motion of a skeleton depends on the major forces that govern its dynamics and cannot be inferred from skeletal geometry alone.     

Terrestrial locomotion in pterosaurs

On the basis of a well‐preserved pelvis of Anhanguera sp. from the Lower Cretaceous (Aptian) of the Chapada do Araripe, Brazil, the problem of terrestrial locomotion in pterosaurs is discussed. A three‐dimensional reconstruction of the pelvis led to a lateral, dorsal and posterior orientation of the acetabula. By use of the preserved proximal ends of the femora of the same individual, the articulation in the hip socket could be tested. The normal articulation of the femur resulted in a horizontal position of the femur shaft, probably during flight. For constructional reasons the femur could not be brought down to a vertical position. Therefore, a parasagittal swing of the femora necessary for a bird‐like stance and gait must have been impossible. It is suggested that in pterosaurs the wing membrane was attached to the upper leg, which helped in stretching, steering and cambering.

Moreover, on the basis of comparisons of the fossil preservation of pterosaurs Compsognathus and Archaeopteryx in the Solnhofen limestone, it is concluded that the femora of pterosaurs were splayed out laterally, and that they had a semi‐erect gait. They were not bipedal animals, but had to use their fore limbs as well on the ground. Nevertheless, as vertebrates extremely adapted to flight, they could not have been able quadrupeds, either.     

Cross-sectional geometric properties of the Otavipithecus mandible

Cross-sectional geometric properties of the postcanine mandibular corpus are determined for the only known specimen of Otavipithecus namibiensis, a middle Miocene hominoid from southern Africa. It is shown that Otavipithecus is unique in that several important mechanical properties of its mandible, including maximum and minimum moments of inertia and distribution of cortical bone, differ from patterns seen in both extant hominoids and the early hominids Australopithecus africanus and Australopithecus (Paranthropus) robustus. This is particularly apparent in the mechanical design of the posterior portion of the mandibular corpus for resisting increased torsional and transverse bending moments. Cortical index values at the level of M₂ also reveal that both Otavipithecus and A. africanus are similarly designed to resist increased masticatory loads with relatively less cortical bone area, a highly efficient mechanical design. © 1996 Wiley-Liss, Inc.