New fossils of dinosaurs known as ornithomimids reveal that the beasts had beaks much like those of modern ducks, according to research reported today in the journal Nature. The findings suggest that rather than hunting for meat as did their carnivorous kin, these ostrichlike dinosaurs used their mouthparts to filter small plants and invertebrates out of the water.

Paleontologists have long debated what ornithomimids ate. Despite the relatively large number of nearly complete skeletons known from these creatures, which belong to the same group of dinosaurs as T. rex and velociraptor, none preserved any soft-tissue structures. As a result, researchers were unable to fully understand what the animals' feeding apparatus looked like and how it functioned. To that end, the new fossils contain valuable clues.

Mark Norell of the American Museum of Natural History in New York City and his colleagues studied two specimens representing two different ornithomimid species. One, Gallimimus bullatus, was discovered last year in the Gobi Desert. The other, Ornithomimus edmontonicus, turned up several years ago in Alberta, Canada. Close inspection of the beaks revealed traces of a keratinous material, much like the keratin found in bird beaks. Furthermore, the researchers found structures in the Gallimimus specimen (right) that bear a striking resemblance to the comb-like "lamellae" in ducks' bills that enable them to strain food from water.

"This is the first time we've seen this structure in a dinosaur," Norell remarks. "It implies a lot about where some ornithomimids lived and what they ate," he adds, noting that fossils of these dinosaurs usually turn up in rocks representing wet environments. "While we can't definitively say that their feeding behavior was just like that of ducks, it is unlikely that the delicate features of their beaks were used for eating large animals."