Wednesday, July 25, 2007

Physical and mathematical modelling gives new knowledge about the feeding habits of pterosaurs

ScienceDaily has an interesting piece about how new research shows that our theories about some pterosaurs' feeding habits have to be re-evaluated.

Feeding Habits Of Flying Reptiles Uncovered

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.

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.

In other words, what we assumed about the feeding habits of these prehistoric creatures is almost certainly wrong, and other ideas have to be tested. Due to the simple fact that these creatures cannot be observed while feeding, we can never be entirely certain about how they feed, but we can at least remove some possibilities, and make a case for the most likely way.

The findings are also interesting because they show that we can't assume anything from just the shape and form and form of the fossils. Something the article also states.

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."

This shows the importance of re-evaluating and testing our ideas frequently. In this case, it probably makes little difference that our assumptions were wrong, but in other cases, those assumptions could be the basis of other assumptions, which would have to be re-evaluated, or maybe even discarded, as an result of the first assumptions being wrong.

Annoyingly, the ScienceDaily article didn't state where the study was published, but I managed to locate it at PLoS Biology
Did Pterosaurs Feed by Skimming? Physical Modelling and Anatomical Evaluation of an Unusual Feeding Method

Author Summary

Just because a component of an extinct animal resembles that of a living one does not necessarily imply that both were used for the same task. The lifestyles of pterosaurs, long-extinct flying reptiles that soared ancient skies above the dinosaurs, have long been the subject of debate among palaeontologists. Similarities between the skulls of living birds (black skimmers) that feed by skimming the water surface with their lower bill to catch small fish, and those of some pterosaurs have been used to argue that these ancient reptiles also fed in this way. We have addressed this question by measuring the drag experienced by model bird bills and pterosaur jaws and estimating how the energetic cost of feeding in this way would affect their ability to fly. Interestingly, we found that the costs of flight while feeding are considerably higher for black skimmers than previously thought, and that feeding in this way would be excessively costly for the majority of pterosaurs. We also examined pterosaur skulls for specialised skimming adaptations like those seen in modern skimmers, but found that pterosaurs have few suitable adaptations for this lifestyle. Our results counter the idea that some pterosaurs commonly used skimming as a foraging method and illustrate the pitfalls involved in extrapolating from living to extinct forms using only their morphology.

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