Samplings: December 2007–January 2008

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©iStockphoto.com/Darren Gidney

Today, only three bird species have the chops to skim for their supper. Black, African, and Indian skimmers fly low, pushing their lower beaks through the water, then snap their jaws shut when they hit a fish. Anatomical similarities between skimmers and pterosaurs—ancient flying reptiles that included pterodactyls—have led some paleontologists to suggest that pterosaurs also ploughed the water’s surface. But Stuart Humphries, now at the University of Sheffield in England, begs to differ. With three colleagues, Humphries made casts of the lower beaks of skimmers and pterosaurs, pulled the casts through water, and measured the drag force water exerted on the beaks. The team calculated that overcoming drag consumes a fifth of the energy that modern skimmers devote to flying—a substantial handicap that probably explains why skimming is so rare. As for the pterosaurs, Humphries measured such great drag on their beaks—as much as 68 percent of what their total energy expenditure would have been, he calculated—that flying while skimming would have been impossible for all but the smallest species. The team also compared the skulls and necks of pterosaurs and skimmers, and discovered that pterosaurs possessed few of the thirty adaptations that enable skimmers to do their thing. It’s more likely, says Humphries, that when the largest flying creatures of all time fished, they snatched their meals from the water in one targeted swoop. (PloS Biology)