Filter feeders suck water that contains food into the back of their mouths, then use their tongues to push the water forward. The fine hairs around the beak trap the food while the animals expell the water out the sides of their beaks.
The researchers studied the remains of two recently discovered ornithomimid skeletons in which the soft tissue structure of the beak was well preserved. The fossils were found in Alberta, Canada, and Tsaagan Khushu, in Mongolia's Nemegt Basin.
The beaks and jaw structures of the fossilized creatures closely resembled those of modern-day ducks, geese, and swans, all of which feed by straining sediment with their beaks.
The finding, combined with previous evidence, led the researchers to conclude that ornithomimids were filter feeders. Gastroidsdirt-filtering gizzard stones, which are common in modern filter feedershave been present in many of the ornithomimid fossils found in China.
Moreover, ornithomimid fossils are abundant in wet environments and extremely rare in arid environments, which is consistent with their being dependent on water, Mackovicky explains.
"It's an unoccupied niche, and it makes sense that some animal evolved to fill it," he said.
Recent National Geographic News stories on dinosaurs:
Study Paints New Picture of Dinosaur's Nose
Skeleton of New Dinosaur "Titan" Found in Madagascar
"Tidal Giant" Roamed Coastal Swamps of Ancient Africa
"Feathered" Fossil Bolsters Changing Image of Dinosaurs
Oddly Angled Teeth Make Masiakasaurus Stick Out
Additional dinosaur resources from National Geographic:
Paul Sereno: NG Explorer-in-Residence and dinosaur hunter
Destinations: Dinosaur National Monument
Educational Video: Dinosaurs on Earth: Then and Now
Children's Pop-up Book: Dinosaur Babies
Related lesson plan
Use this National Geographic News article in your classroom with the Xpeditions lesson plan: Physical Characteristics of Places: The Fossil Record
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