A new species of dinosaur discovered in Utah is providing paleontologists with clues to how some of these ancient carnivores gave up meat and adopted a vegetarian lifestyle.
The first dinosaurs were carnivores. During their evolutionary history, many kinds of herbivores evolved, such as the horned triceratops and the giant sauropods. The new critter, named Felcarius utahensis, is a peculiar misfit. It was the only vegetarian member of a group of highly specialized predators called the theropods, which sported long legs and tails, slim bodies, and razor-sharp teeth. Therizinosaurs were most closely related to deadly Velociraptor-like dinosaurs.
The transition from meat-eating predators to that of the plant-eating therizinosaurs has been a mystery because of gaps in the fossil record. The 125 million year old Felcarius, discovered by paleontologist James Kirkland at the Utah Geological Survey and colleagues, helps fill in the holes. More than 1700 bones recovered from a 2-acre site about 3 hours from Salt Lake City indicate that the animal embodied the physical features of both its carnivorous ancestors and its plant-eating descendents: The 4-meter tall beast had a long tail and sickle-shaped claws, but it also had teeth shaped for shredding plants and a wider pelvis, which made room for the larger gut needed to digest plants. In addition, it walked on two legs that were shorter than its Velociraptor-like ancestors but not as short as later therizinosaurs.
"This animal is an example of evolution in action," says Scott Sampson, a paleontologist at the Utah Natural History Museum and coauthor of the study published 5 May in Nature. "We can now state with some confidence that this odd group of predators evolved by first changing their diet and later changing parts of their skeleton," he adds. "But whether Felcarius was a devoted vegan or an omnivore, we can't say." One reason for the animals' dietary shift could have been the appearance of a new food source--flowering plants--which arose around the same time Felcarius lived.
Peter Makovicky, a curator of dinosaurs for The Field Museum in Chicago, says the findings definitely help fill in important gaps in the fossil record. "With this animal, we have some dates for when this group evolved and by which time it would have evolved certain features," he says. "Now we can start answering questions about the evolutionary timing of therizinosaurs."