How Pterosaurs Ate - It Wasn't Skimming
    By News Staff | July 23rd 2007 10:22 PM | 1 comment | Print | E-mail | Track Comments
    Scientists at the University of Sheffield, collaborating with colleagues at the Universities of Portsmouth and Reading, have taken a step back in time and provided a new insight into the lifestyle of a prehistoric flying reptile.

    Using new physical and mathematical modelling, Dr Stuart Humphries from the University of Sheffield, along with scientists from the Universities of Portsmouth and Reading, has shown that suggestions that extinct pterosaurs gathered their food by ‘skimming’ the surface of the ocean with their beaks are inaccurate.

    Physical and theoretical models show that pterosaurs (Thalassodromeus, right) could not meet the energy requirements of skimming, a rare feeding strategy practiced habitually by just a few extant Rynchops species(black skimmer, left). Credit: Mark Witton, University of Portsmouth

    Previous studies have suggested that some pterosaurs may have fed like modern-day ‘skimmers’, a rare group of shorebirds, belonging to the Rynchops group. These sea-birds fly along the surface of lakes and estuaries scooping up small fish and crustaceans with their submerged lower jaw. Inferred structural similarities between pterosaur and Rynchops jaws had previously been used to suggest that some pterosaur were anatomically suited for skimming.

    However, new evidence provided by the researchers suggests that the fossilised jaws of suggested pterosaur skimmers mean that these creatures may have found it impossible to feed in this way.

    According to the research, the thicker jaws of pterosaurs would make it difficult for them to deflect water the way the extraordinarily slim bills of Rynchops do. By combining experiments using life-size models of pterosaur and skimmer jaws with hydrodynamic and aerodynamic modelling, the researchers demonstrated that skimming requires more energy than the giant reptilian fliers were likely able to supply.

    The researchers established that pterosaurs weighing more than one kilogram would not have been able to skim at all. They also found that anatomical comparisons between the highly-specialised skull of Rynchops and those of postulated skimming pterosaurs suggest that even smaller forms were poorly adapted for skim-feeding. They believe that the pterosaurs they studied would have in fact fed using more conventional methods.

    The size and body plan of these long-extinct animals can be reliably reconstructed from fossils, as can their time of existence on Earth. As a result of this evidence, scientists know that pterosaurs had membrane-covered wings like bats. Their extremely light, hollow skeletons were presumably filled with air, allowing even pterosaurs with wingspans in excess of 10 m to take to the skies, which they began to do as far back as 230 million years ago.

    Discovering the ecological traits of these reptiles though is far more complicated. One way scientists currently gain an insight into ecological traits of extinct animals is by comparing fossilized morphological (shape and form) features to those of living animals.

    However, as this new research shows, these records do not provide direct evidence of behaviour and ecology. Dr Humphries, from the Department of Animal and Plant Sciences, said: “Our results illustrate the pitfalls involved in using morphological data to study the ecology of extinct animals, including dinosaurs and pterodactyles.”

    “While we acknowledge that these comparisons do offer clues to the ecological traits of extinct creatures, we hope that our research shows that biomechanical analysis is also needed to supplement such efforts in order to paint a more realistic portrait of the prehistoric landscape."

    The researchers involved in the project are: Dr Stuart Humphries, University of Sheffield; Dr Richard Bonser, University of Reading; Mark Witton, University of Portsmouth and Dr David Martill, University of Portsmouth.


    Fossil Huntress
    Pterosaurs were skilled arial hunters, catching their prey on the wing. Pterosaurs, the mighty winged-lizards, soared ancient skies expertly hunting for prey.

    Because they evolved from reptiles prior to modern birds, it was once believed that pterosaurs were primitive, passive fliers. They were seen as gliders, rather than skillfull hunters. Being the earliest vertebrates to have evolved powered flight, we now recognize that they were powerful fliers, chasing and catching their prey on the wing. One clue to this revelation is a small bone at the front of the wing bone which curves back towards the shoulder, roughly like an elongated thumb on a spread hand.

    Modern birds have a small but vital feather, the aula, in this position. It shifts, acting like the leading edge on some airplane wings, redirecting the airflow over the wing, and allowing major changes in speed and angle in the air for comparatively little effort. It seems clear the pterosaurs’ extended thumb would have held a flap of membrane in a similar position at the front of the wing, and for a similar purpose.