What did Deinonychus really do with its feet? John Ostrom initially painted the picture of a fleet-footed predator, chasing down prey animals and slashing at them with the enlarged claw on its second toe. To take it from Crichton, they were slitting bellies and dancing in spilled viscera. A few years ago, Phil Manning of the University of Manchester suggested they were more likely "climbing crampons," allowing them to cling to the panicky tenontosaurs they were attacking. In a new PLoS One paper, Denver Fowler, with Elizabeth Freedman, John Scannella, and Robert Kambic, puts forward another option: they were grasping tools for holding down smaller prey (or, in typically colorful science-speak, prey of "subequal body size".
To come to this conclusion, Fowler and team compared the feet of Deinonychus to other animals: a diverse group of extinct theropod genera as well as living birds. When compared to dinosaurs, the proportions of their feet differed strikingly from ornithomimids and alvarezsaurs, both groups whose leg proportions strongly suggest a cursorial lifestyle. They were runners. As Matt Martyniuk recently wrote in an excellent DinoGoss post, the sticky assumption that dromaeosaurs were particularly quick animals, chasing down prey, isn't really supported by the evidence. Noting that Ostrom's first ideas changed once he took full stock of the proportions of Deinonychus's metatarsus length to its tibia length, Matt writes, "Not only was Deinonychus not particularly fast, it probably could not have been nearly as fast as most other small theropods, including modern flightless birds, let alone cheetahs."