When James Kirkland first walked the barren, mudstone hilltop in the Utah desert four years ago, he was stunned by how many fossils littered the ground.
His excitement was tinged with regret, however. Dr. Kirkland knew that his guide, Lawrence Walker, was sharing a secret that probably would lead to Mr. Walker's prosecution for taking dinosaur bones from the site. It was federal land. And Walker, a commercial collector, had no permit to dig there. But Walker also sensed he'd found something truly remarkable on this remote patch of sandstone buttes and mesas. He agreed to lead Kirkland - Utah's state paleontologist - to the site and risk the consequences.
"I was overwhelmed," Kirkland recalls. "I put my hand on his shoulder and told him: 'I'll have to give a deposition if I'm asked to, but I am very grateful you chose me' " to see the site.
Grateful indeed. A team of paleontologists led by Kirkland announced Wednesday the discovery of a new dinosaur caught in the evolutionary act of shifting from a meat eater to a vegetarian.
The 125-million-year-old creature is expected to shed light on this process not just for the dinosaur's group itself, but for dinosaurs generally, the researchers say.
Moreover, its appearance in North America may deal a blow to the idea that the group originated in Asia. And it may become one of the most thoroughly studied dinosaurs in history. The hilltop is a mass burial ground for the animals. The new find, dubbed Falcarius utahensis, may have hundreds of its brethren interred there in well-preserved condition.
In the world of paleontology, that's a big deal. The overwhelming majority of the roughly 900 dinosaur species known are represented by a partial skeleton or a few bone fragments, Kirkland explains. "We estimate that there are well over a million bones here, and 99 percent are from this animal," he says. "This animal will be a hallmark dinosaur one day."
In its heyday, Falcarius measured 13 feet from beak to tail. It stood 4-1/2 feet tall and boasted talons four inches long. To the uninitiated, it resembles its Velociraptor cousin in many ways. But on closer inspection, the creature is clearly demoting itself on the food chain, the researchers say. Its teeth are losing their meat-eating edge. Its pelvis is broadening to accommodate a digestive system large enough to handle a plant-based diet. Its neck is growing longer, its legs stubbier, and its head smaller. In all, Falcarius displays 20 features of plant-eating dinosaurs that it appears to have evolved independently from other herbivores, according to Lindsay Zanno of the University of Utah, who is working on the project.
Described in the team's formal report in Thursday's edition of the journal Nature, Falcarius belongs to a group of dinosaurs known as therizinosaurs. The group is a dead-end branch off of an evolutionary path that led from an ancestor shared with Velociraptors to modern birds.
Falcarius appears to be the primitive forerunner of Therizinosaurus, a creature Mrs. Zanno calls "a Frankenstein of the dinosaur world." Therizinosauruses roamed what is now the Gobi desert between 94 and 65 million years ago. Nearly 30 feet long, they sported claws of up to 28 inches; Zanno describes them as a cross between an ostrich, a gorilla, and Edward Scissorhands.
Finding its ancestors clustered in the Utah desert will provide a goldmine of information, she says. "We have bones from babies, juveniles, and adults. We have males and females. This will allow us to conduct biological and population studies for a species that went extinct 125 million years ago."
How so many creatures came to be clustered in one place is a mystery. Zanno notes that the animal remains appear to have accumulated in three events separated by at least 1,000 years. The area shows no evidence of volcanism at the time. Nor is there evidence of raging rivers, which might have trapped large numbers of animals trying to cross. The team speculates that Falcarius herds might have perished after drinking at a pond or small lake tainted by carcasses or algae blooms.
And why would a creature begin to slide down the food chain? It may be the result of broader ecological changes taking place at the time, says Scott Sampson, chief curator of the Utah Museum of Natural History at the University of Utah in Salt Lake City. Sampson, along with Donald DeBlieux from George Washington University in Washington, D.C., is a member of the research team reporting the results.
He explains that 125 million years ago, Earth was undergoing an extended warming period and lacked permanent ice caps. Continents were breaking apart from the supercontinent Pangea. And plant forms were expanding from ferns and conifers to flowering plants.
This explosion in plant life gave animals "a whole new set of fodder," he says. Falcarius may have eased its way into an unfilled ecological niche that allowed its lineage to survive for some 50 million years.
For Kirkland, the site was like a gift. He'd been working on fossils from the same broad rock formation elsewhere in Utah. And in the late 1990s he uncovered fragmentary remains of the first therizinosaur found in North America; he called it Nothronychus. It was 90 million years old. Now, at 125 million years, Falcarius is as old as any therizinosaur found in Asia, raising questions as to where the line originated.
Without Walker's portentous invitation to visit the what's now called the Crystal Geyser Quarry, "we never would have found it, at least [not] for 100 years or so," Kirkland acknowledges.
In November 2002, Walker was indicted on charges of theft of government property. He served a five-month prison term and has returned to his home in Moab, Utah. Kirkland says that Walker has asked to help excavate the fossils as a volunteer.
"He has paid his dues," Kirkland says. "So I told him he is welcome to volunteer on the project."