for National Geographic News
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."
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."
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