Pterosaurs – flying time machines Dr Dave Martill, Reader in Palaeobiology, School of Earth and Environmental Sciences, University of Portsmouth I am going to talk to you about a group of animals that are really pterosaur. There are a few animals that have been suggested as quite fascinating for all sorts of reasons but mainly because they possible ancestors but analysis of their skeletal structure has gen- can fly. We have a lot to learn from pterosaurs because they are erally ruled them out; so we do not know from which group they so beautifully engineered and in this talk I am going to examine evolved. At the end of the Cretaceous they disappear very sud- aspects of their anatomy and discuss their diversity and history. denly, and at the same time that the large dinosaurs disappeared. So they too had a pretty good innings in the sky and it is rather Now of course we can fly (in aeroplanes); but this is expensive in sad that they did not leave any descendants. Similarly there is no terms of the energy required to do it. Flight has evolved several animal alive today that we can recognise as being descended from times in the animal kingdom but man has had to do it through cul- an animal that was the putative ancestor of pterosaurs. So, in tural means and the use of technology. Flight (powered flight, not terms of their relationships to other animals, there are still many gliding) first evolved in the Carboniferous invertebrate world of unanswered questions and we are only able to examine their flight the insects. No other invertebrate group has evolved active pow- by analysis of their meagre fossil record. ered flight. How did they do it? Well we know that they grew wings but they had to evolve wings from something; perhaps they A study of their anatomy is made all the more difficult as they evolved from lateral appendages such as gills. Larval have undergone so many skeletal modifications for flight that try- ephemeroptera have gill structures which are superficially wing- ing to work out from which group of animals they derived has like but they are lateral membranes with veination and functions always been problematic. Indeed, in the early days, when as gills, but it can be imagined that if they thickened and length- pterosaurs were first discovered, they were put into all sorts of ened they would come to resemble wings. groups and it took quite a long time before they were recognised as flying animals. Despite the fact that Cuvier had determined We are all familiar with birds who fly very beautifully and grace- that pterosaurs had been flying animals and were reptiles, a fully; there are all sorts of controversies about how birds gained reconstruction in the 1830s depicted pterosaurs as aquatic and the power of flight. It is relatively easy to examine and under- supposed that their elongate fourth finger was enclosed in a large stand the anatomy of the bird skeleton and we can work out what paddle as in some turtles; quite clearly this reconstruction failed skeletal modifications had to take place in order to develop their to consider the stresses that would be applied on these joints at the wing. From this and from good fossil evidence, it would appear distal end of a paddle when rowing through the water. One stroke that birds are derived from small theropod dinosaurs. Many small and it would have broken the finger in several places. Yet anoth- theropod specimens have been found in China that have struc- er reconstruction depicted pterosaurs as a type of marsupial bat; tures in the integument that may be interpreted as proto-feathers, however, it was based on evidence that pterosaurs possessed fur feather-like structures or even true feathers. Controversies arise which has since been supported by more recent discoveries. The over why feathers evolved in the first place. Did feathers evolve presence of fur is supported by recent discoveries, but clearly simply for flight? The answer is almost certainly "No". Did they they were not marsupials. have some other purpose? The answer is almost certainly "Yes". Could it be for insulation? That would allow dinosaurs to have The anatomy of pterosaurs is rather bizarre. There are broadly evolved small bodies; if they could insulate themselves they two types of pterosaur; long tailed forms and short tailed forms, could have small bodies without losing heat and that would have the so-called rhamphorhynchoids and pterodactiloids respective- allowed them to become nocturnal. Perhaps they evolved feathers ly. Pterosaurs look head heavy with massive skulls compared for sexual display and they became secondarily co-opted for with their relatively tiny bodies (Figure 1). The body is usually flight. The late Jurassic Archaeopteryx from Solnhofen, Germany, considerably shorter than the skull and those forms with large shows beautiful impressions of feathers on an ordinary dinosauri- an–type hand and a dinosaurian-like tail, clad in feathers. There have to be some ancestors to this animal that also possessed feath- ers, perhaps somewhere in the Lower Jurassic, although none has yet been found. Bats are another group of vertebrates that achieved active pow- ered flight; with a record going back into the Eocene. Thus bats have been flying for around about 55Ma while birds have been flying for probably 145Ma and quite likely a bit longer. Insects, on the other hand, have probably been flying for nearly 400Ma. Insects, bats and birds are still with us and still flying but pterosaurs, flying reptiles of the Mesozoic, were first on the scene towards the end of the Triassic but became extinct at the end of the Cretaceous. They seemingly appeared from nowhere about 220Ma ago: the first pterosaurs in the fossil record are fully developed flying animals; there are no intermediate animals Figure 1. Scaphognathus crassirostris, a long-tailed between a ground-dwelling four-legged animal and the flying pterosaur. Photo Dino Frey. OUGS Journal 23(2) 1 Symposium Edition 2002 Figure 3. Close up of the skull of Scaphognathus cras- sirostris showing the holes in the skull and the widely spaced teeth. Photo Dino Frey. long piece of bone. In a meat-eating dinosaur there is an articula- tion which allows for the absorption of shock when biting. Pterosaurs do not have this articulation so in this they differ from Figure 2. Anhanguera. Note how small the pelvic girdle is com- many reptiles. The eye was very large; that fits with an animal that pared with the pectoral girdle. Notice also that the skull is is an active flyer, it surely needed to see where it was going, it longer than the body. Wing span ~5m. Photo Dino Frey. needed to be able to see where its prey was so presumably had acute vision. They are assumed to have been pursuit predators or crests look top heavy; but they are not - they are very lightly con- fishers. structed. Nevertheless, it is the feeding end and pterosaurs need- ed an apparatus for catching food. They had to feed using only Two holes in the back of the skull show that pterosaurs belong to their mouths as their hands were attached to the ends of very long a group of reptiles called the diapsids. Pterosaurs are not arms and their wings could not be used for manipulating food. All dinosaurs but they belong in a group which includes dinosaurs food gathering had to be done by the mouth. and crocodiles and that group is called the Archosauria. A lot of workers consider pterosaurs as the sister group to the dinosaurs, Pterosaurs had a small pelvis; all the elements of the pubis are meaning that they are more closely related to dinosaurs than they fused together as are the vertebrae of the sacrum forming a rigid are to crocodiles. Recently it has been suggested that pterosaurs box-like structure into which the rear limbs lock (Figure 2). This lie outside the Archosauria and are not as closely related to the is the business end for landing. The vertebrae just behind the neck dinosaurs as previously thought. Yet another aspect of controver- and through the thorax are all fused together, as are the adjacent sy in pterosaurs. ribs and the neural spines making it very heavily braced. The backbone is locked tight, also forming a very rigid box-like struc- Let us consider the skull in a bit more detail. It has a large eye and ture, with the shoulder girdle in which the lower two elements, the the eyeball is supported by a sclerotic ring, there is the antorbital coracoids, are often fused to the upper two elements, the scapulae, fenestra (with the nostril). In many pterosaurs with teeth the den- forming a very rigid circular structure encasing the backbone on tition is elongate and very widely spaced (Figure 3). Such teeth which to anchor a pair of wings. are no use for processing food in the mouth: prey was simply caught and swallowed, so the mouth is really a trap that took fish There are generally a lot of similarities between rhamphorhyn- from the water. It was thought that they were biting the fish but choids and pterodactyloids, but there are a few small differences then the fish would be impaled on the largest teeth and they had which are to do with the ratios of different components in the no means to get them off. wing: for instance the metacarpal is very short in rhamphorhyn- choids whilst in most pterodactyloids it is exceedingly long. The skeleton of the arms of pterosaurs contain many elongate There are some differences, probably related to flying manoever- bones; on the humerus a delto-pectoral crest projects forwards ability and speed, in the shapes of the humerus and especially in operating as a lever for the attachment of flight muscles to the the skull, but essentially the body form is rather conservative.