Among the strangest of the theropods was a type of dinosaur called the therizinosaurs. When the first huge sickle-like claws were found in Mongolia in 1948, scientists thought it was a giant turtle. Other fossils found more recently led to its classification as a strange form of theropod in 1993, said Currie.
"They have huge, sharply pointed claws more adapted for meat eating, but they have teeth that are leaflike, adapted for plants or maybe fish," he said. Some paleontologists think the claws were used for ripping apart termite nests to feed on the insects; others think the dinosaurs were herbivores.
Other odd features of therizinosaurs include birdlike hips and long ostrichlike necks. Recent finds include impressions left by feathers, which helps their grouping with theropodsthe possible ancestral relatives of birds.
"Therizinosaurs look like dinosaurs built by committee," said Holtz. "There are bits and pieces made by every animal."
Other interesting theropods on Holtz's list include Shuvuuia and Mononykus from Mongolia. These chicken-sized dinosaurs with small, beaky heads and long necks had the unusual characteristic of short arms and only one functional finger. "No one has come up with a reasonable explanation for these forelimbs," said Holtz.
Another dinosaur on Kirkland's list is Utahraptor, a giant lizard-like dromaeosaur that lived about 100 million years ago during the early Cretaceous period. Kirkland's recent work on Utahraptor shows that it had huge, powerful legs with clawed feet, which it used to kick down and puncture the hides of the dinosaurs it ate.
"Nothing had the kick force it had," said Kirkland. "It could rip through a hide an inch thick or more."
Living at the same time as Utahraptor was a dinosaur that belonged to the tanklike armadillo shaped ankylosaurs called Gastonia. It had enormous spikes on its shoulders and armored plates along its neck, body, and tail, making it what Kirkland calls the most well protected dinosaur that ever lived.
"It makes a lot of sense that co-existing with Utahraptor would be the most heavily armored dinosaur," he said. "They formed part of an ecosystem that was stable and maintained itself for probably several million years."
Mark Norell, curator and chairman of the division of paleontology at the American Museum of Natural History in New York, said that another weird dinosaur is a sauropod from Argentina called Amargasaurus that lived during the early Cretaceous period.
Amargasaurus was 33 feet (10 meters) long and was built mostly like a typical sauropod: a four-legged, heavy bodied herbivore with a small head and long neck and tail. Oddly, though, it had two rows of spines growing out along its neck, body, and tail that may have been encased in skin to form a huge sail that regulated body heat or served as an ornament to attract mates or ward off predators.
"Dinosaurs in general were anatomically a lot more diverse than most people give them credit for," said Norell. "You never can expect what you are going to find next."
More National Geographic News Stories on Dinosaurs:
Dino Dung: Paleontology's Next Frontier?
Do They Really Look Like That? The Science of Dino Art
Dinosaur Footprints: Tracks Tell Prehistoric Secrets
Four-Winged Dinosaurs Found in China, Experts Announce
Utah Dinos May Have Been Killed By Drought
Cuban Dinosaur: First Confirmed Remains Discovered
Dinosaur Cannibal?Mystery in New Mexico
Tetrapod Fossil FoundFirst Ever in Asia
New Picture of Dinosaurs Emerging
Fossil Implies Our Early Kin Lived in Trees, Study Says
Weird Buck-Toothed Dinosaur Found
Dinosaur Tracks Preserved on Scottish Island
Dinosaur Tracks Shed Light on Sauropod Evolution
Comets May Have Led to Birth and Death of Dinosaur Era
Fossil of Dog-Size Horned Dinosaur Unearthed in China
Tyrannosaurus rex Was a Slowpoke
Researchers Rethink Dinosaur Die Off Scenario
Researchers Melt Polar Dinosaur Mysteries
Scientist's Finds Spur New Thinking on Dino Evolution
Dino-Era Vomit Fossil Found in England
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
New Find: Pterosaur Had Strange Crest, Fishing Style
Dinosaur Beak Probably Used to Strain Food, Not Kill Prey
Additional Dinosaur Resources from National Geographic:
RELATED LESSON PLANS
Use this National Geographic News article in your classroom with these Xpeditions lesson plans and student activity:
K-2: Dinosaur Bodies
3-5: How Do Scientists Find Dinosaur Fossils?
6-8: The Science of Digging Up Dinosaurs
9-12: The Evolution of Dinosaurs Over Geologic Time
K-2: Those Fussy Dinosaurs!
9-12: Physical Characteristics of Places: The Fossil Record
Activity: A Dinosaur's Neighborhood
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