Dinosaur Beak Probably Used to Strain Food, Not Kill Prey

Hillary Mayell
for National Geographic News
August 29, 2001
Researchers studying the fossil remains of two beaked dinosaurs have
concluded that the animals probably used their beaks to sieve food
rather than as a weapon to attack predators for meat.

If the finding is correct, the beaked dinosaurs known as ornithomimids would be the largest known land-living creatures that filter their food in eating. Modern-day filter feeders include flamingos and ducks.

Ornithomimids, which lived during the Cretaceous period, from 144 to 65 million years ago, could be as long as 20 feet (7 meters) and weigh up to 1,000 pounds (450 kilograms).

Although commonly known as ostrich mimics because of their appearance, they were not closely related to birds. Instead, ornithomimids belong to the theropod family of mostly carnivorous dinosaurs, which also included species such as Tyrannosaurus rex.

Early members of the ornithomimid group didn't have a full beak and had some teeth. Later ornithomimids that evolved looked somewhat like the modern-day ostrich. They were very fast and had large eyes and toothless, beaked mouths.

"There has been a great deal of speculation about the dietary habits of these dinosaurs over the last 80 years since the first reasonably complete skeleton was found," said Peter Mackovicky, a paleontologist at the Field Museum in Chicago. "Other features indicated they were related to predators, but the beak stumped people."

Unknown Function

Until now there have been two theories about the function of the dinosaurs' beaks. One theory held that they were used to eat small prey, such as lizards. Other scientists have speculated that the dinosaurs might have been herbivorous, eating leaves and fern fronds, and used their beaks for foraging activities such as stripping bark from trees.

In the August 30 issue of Nature, Mackovicky and paleontologists Peter Norell of the American Museum of Natural History and Philip Currie of the Royal Tyrrell Museum in Canada propose a novel explanation: that the ornithomimids were filter feeders, like today's flamingos.

"Nobody predicted they might be straining their food," said Mackovicky. "It's a somewhat unexpected finding, but consistent with other evidence."

Watery Habitat

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. Gastroids—dirt-filtering gizzard stones, which are common in modern filter feeders—have 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
Wanted: Albertosaurus
Dinosaur Eggs
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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