Some dinosaurs were like prehistoric tanks on four legs protected by bony armor and huge tails that could swat away an attacker.
Two new species of these heavily armored dinosaurs have emerged from an unusually productive Utah fossil bed near the College of Eastern Utah in Price, about 100 miles southwest of Salt Lake City.
The species, both 30 feet long, are an Ankylosaur, or club-tailed armored dinosaur that's the oldest ever found, and a clubless armored dinosaur or Nodosaur, the biggest on record.
James Kirkland, incoming state paleontologist for the state of Utah, has worked the fossil bed for more than a decade, piecing together discoveries that provide clues to life 100 million years ago.
"You're going to see a lot of animals coming out of here," said Kirkland, referring to the Utah location.
Kirkland displayed bone casts of the discoveries Monday. The actual bones of the plant-eaters are kept at the College of Eastern Utah Prehistoric Museum.
He said the species would be officially named when the findings are published in the coming year. Kirkland will analyze the bones with Kenneth Carpenter, a dinosaur paleontologist with the Denver Museum of Natural History.
Ankylosaurs and Nodosaurs are ankylosaurids, heavily armored dinosaurs that originated in the Jurassic Period but are more common in the Cretaceous, the last dinosaur period.
The ankylosaurids are mainly from Asia and are believed to have crossed a land bridge to North America. "There are some Asian animals very similar to this," Kirkland said. "This is really dating the first animals coming in from Asia."
Carpenter said the Ankylosaur discovery pushes back the date of the land bridge some 20 million years to about 110 million years ago. The dating was done through volcanic ash known to be 98 million years old.
Robert M. Sullivan, senior curator of paleontology and geology at the State Museum of Pennsylvania in Harrisburg, called the findings exciting and said the large Ankylosaur, nearly 50 percent bigger than others previously found, shows that the dinosaur family is more complex than originally believed.
But, Sullivan said, the discoveries would be hard to assess until published findings are available.
Mark Norell, chairman of the department of vertebrate paleontology at the American Museum of Natural History in New York, agreed that the size of the Ankylosaur was significant.
The Cleveland Museum of Natural History was selected for the announcement because it is hosting a dinosaur exhibit which produces proceeds that help finance dinosaur research through the nonprofit Jurassic Foundation.