No Skimming Allowed

Abstract

BIOMECHANICS Pterosaurs were flying reptiles and the first air-borne vertebrates; they dominated the skies from the late Triassic to the end of the Cretaceous, during the epoch of their relatives, the dinosaurs. On the basis of similarities in jaw structure, it has been suggested that several pterosaurs, including Thalassodromeus and the giant Quetzalcoatlus (with a wingspan of up to 15 m), could have fed by skimming in a manner akin to that of extant ternlike shorebirds ( Rynchops spp.) Skimmers fly low over calm shallow water with the tip of their lower beak dipping beneath the water surface. Humphries et al. have used full-sized models of mandibles from Thalassodromeus and the modern skimmer R. niger to demonstrate that the pterosaur bill would have generated an order of magnitude more drag in traveling through the water. Modeling indicated that the energetic cost to a shorebird of flying with its beak in the water is almost prohibitive (~20% of the total cost of flight), and the authors suggest this levy might explain the rarity of the skimming life-style. The substantially greater cost for a pterosaur larger than 2 kg appears to exclude outright skimming as a possible means for procuring food. Furthermore, many of the morphological specializations to the head and neck seen in Rynchops are not found in pterosaurs of any size, including the ability to regenerate broken or abraded bill tips and the presence of a reinforced lower jaw. — GR PLoS Biol. 5 , e204 (2007).