Ongoing projects and interests of the Animal Flight Group

Department of Zoology, University of Cambridge

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Pterosaur flight.

My research focuses on the flight of the extinct pterosaurs: a group of reptiles, contemporaneous with the dinosaurs, that dominated the skies during the Mesozoic era. Their wings were membranous, supported in the main part an enormously elongated fourth finger. The wing construction is relatively simple when compared with that of the birds and bats, yet pterosaur flight has received little attention since the discovery of the group just over 200 years ago. This is mainly because, until recently, the available fossil material has not been of sufficient quality to permit an accurate three-dimensional reconstruction of the skeletal anatomy: a prerequisite for a thorough biomechanical analysis. Pterosaur bones were very fragile, so fossil remains are almost always found in a flattened state. However, a locality was discovered in Brazil some 30 years ago - the Santana Formation - from which a number of exceptionally well-preserved specimens have been unearthed. In some cases, nearly complete skeletons have been found in their original three-dimensional condition. Such fossils are ideal for an analysis of pterosaur flight.

Recently I have investigated the gliding flight of a Lower Cretaceous family of pterosaurs called the Ornithocheiridae, a group that is particularly well represented in the Santana Formation. By using a novel technique to rearticulate exceptionally well-preserved fossils I determined the 3D spatial orientation and range of movement of the wing skeleton of a typical ornithocheirid: Anhanguera. The results of this study are presented as video clips below, showing the complete, fleshed out pterosaur in the postulated gliding position and how it would have folded its wings when on the ground. Of particular note is the orientation of the pteroid bone: a spar-like element, unique to pterosaurs, that articulated at the wrist. Previous workers have generally assumed that this bone pointed towards the body, and so supported a rather narrow forewing with little facility for adjustment. This interpretation is understandable, because this is how the pteroid is oriented in articulated, flattened fossils. However, the 3D Santana fossils show that the bone could be directed forwards, in which case it would have supported a very broad forewing that could have functioned as a leading edge flap.

Animations highlighting the reconstruction: click on the images below to access them.

(AVI file, 3.5 Mb. © Matt Wilkinson 2003. May take time to download.)

(AVI, 1.77 Mb. © Matt Wilkinson 2003. May take time to download.)

I tested the aerodynamic consequences of this new reconstruction by testing wing profile models in a wind tunnel in the Department of Engineering. The results were extraordinary. When standardised with respect to airspeed and wing area, the maximum lift force developed by the pterosaur wings was found to be about 25% higher than that measured for extant flying vertebrates. This high-lift capability would have enabled the ornithocheirids to glide very slowly and may have been instrumental in the evolution of large size by the pterosaurs, the biggest of which had wingspans up to 12m. The leading edge flap could also have functioned as a useful control surface in flight.

Future work will focus on how the aerodynamic effects revealed by the 2D profile tests relate to the performance of the 3D wing. In addition to testing the effects of the forewing, I will also look at another curious feature of pterosaur wings revealed by the recent discovery of exceptionally well preserved soft tissue fossils. These indicate that the pterosaur wing membrane was not a mechanically homogenous structure, but had a relatively elastic inner section and a stiffer distal section, supported by densely packed parallel fibres. I will also investigate stability and control by building radio-controlled gliding models to test in free flight, there being no better trial of one’s understanding of the flight of an animal than the challenge of reproducing it with an accurate working model. The objective of these experiments will be the achievement of steady gliding flight using only those control systems that would have been available to the living animal. The final models will therefore not possess the usual elevators, ailerons and rudders of most man-made aircraft.

The pterosaurs were a morphologically diverse group of animals, and one can be certain that this diversity would have been reflected in their flight adaptations. The ornithocheirids were marine soarers, with a lifestyle equivalent in many ways to that of the modern frigate birds. I will now turn my attention to other groups, using the techniques developed for the ornithocheirids to deduce their modes of flight. Of particular interest is the Azhdarchidae, an Upper Cretaceous family that included the largest of all pterosaurs, because of their importance in relation to our understanding of the size limits of animal flight.

Funding: BBSRC, Clare College Research Fellowship

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Last updated July 2004
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