As flowers bloomed, dinos
went soft, finds suggest
Posted May 4, 2005
Courtesy Utah Geological Survey, University of Utah
and World Science staff
A convicted fossil thief has helped scientists
find a bizarre, feathered dinosaur species that they say seems to have been
making an evolutionary transition from killer to vegetarian. And the changeover would have occurred around when flowers originated, which may be no coincidence, the researchers add.
|This artist's conception shows the bird-like feathered dinosaur
Falcarius utahensis. A mass graveyard with fossils of hundreds
or thousands of the creatures was found in Utah. The small, 4.5-foot-tall dinosaur lived 125 million years ago and represents a missing link between earlier, vicious meat-eaters and later,
plant-munchers, researchers say. (Credit: Mike Skrepnick.)
The dinosaur, dubbed Falcarius
utahensis, was unearthed at a mass graveyard of bird-like, feathered dinosaurs in Utah. The discovery is described in tomorrow’s issue of the research journal
Scientists don’t yet know if the animal ate meat, plants or both, said James Kirkland,
a paleontologist at the Utah Geological Survey and principal scientist for the new study.
But “Falcarius shows the beginning of features we associate with plant-eating
dinosaurs.” This includes smaller teeth; wider hips, which could accommodate the bigger gut
needed for digesting plants; and changes in the legs that would let them carry a bulky body instead of running fast after prey.
The adult dinosaur walked on two legs and was about 13 feet long (4 meters) and stood 4.5 feet tall (1.4
meters), scientists said. It had sharp, curved, 4-inch-long (10 centimeter) claws.
Falcarius, which dates to the Early Cretaceous Period, about 125 million years ago, belongs to a group of dinosaurs known as
therizinosaurs, which also includes feathered dinosaurs found in southeast China in recent years. Falcarius appears to represent a middle stage between deadly carnivores and later, plant-eating
therizinosaurs, the researchers said.
The therizinosaurs are a subdivision of a group called maniraptorans, from which birds are thought to have evolved. The maniraptorans also include sharp-clawed meat-eaters such as
Velociraptor, the dinosaur popularized by chasing children through a kitchen in the hit film “Jurassic Park.”
Falcarius “is the most primitive known therizinosaur,” said study co-author Lindsay
Zanno, a graduate student in geology and geophysics at the University of Utah. Falcarius and Velociraptor had a common, yet-undiscovered ancestor, said study co-author and paleontologist Scott Sampson, chief curator at the Utah Museum of Natural History and an associate professor of geology and geophysics at the University of Utah.
“We know that the first dinosaur was a small-bodied, lightly built, fleet-footed predator,” he added. “Early on, two major groups of dinosaurs shifted to plant-eating, but we have virtually no record of those transitions. With
Falcarius, we have actual fossil evidence of a major dietary shift, certainly the best example documented among dinosaurs. This little beast is a missing link between small-bodied predatory dinosaurs and the highly specialized and bizarre plant-eating
Kirkland, the leader of the research group, found the site of the newfound dinosaur species in 2001 thanks to a fossil collector who later was convicted of fossil theft.
“We never would have found it, at least for 100 years or so, if he hadn’t taken us to the site,” Kirkland said. “Once he figured out he had a new dinosaur, he realized scientists should be working the site. His conscience led him to get this stuff to me.”
The story began in 1999, when Kirkland, who was working in Colorado, received the bones from people who had brought them at a fossil show. A fossil enthusiast later gave Kirkland rough directions to the therizinosaur site, but Kirkland could not find it. So the hobbyist introduced Kirkland to a collector named Lawrence Walker, who had taken fossils from the site.
Walker led Kirkland to the site.
Kirkland then applied for a digging permit from the federal government, which asked Kirkland to provide information about Walker’s activities In November 2002, Walker was indicted in U.S. District Court in Salt Lake City for theft of government property. He pleaded guilty, was sentenced to five months in prison and 36 months of supervised release, and was ordered to pay $15,000 in restitution. He served his prison time in 2003 and then returned home to Moab, Utah.
Although Walker led Kirkland to the site, “we simply can’t justify illegal activity because it might let us know of something we might not know otherwise,” Sampson said.
“Illegal commercial collection of fossils has become a major problem globally,” he added. “Many highly significant specimens, a number of which represent animals brand new to science, are being lost to private collections.” This “robs not only the scientists, but the general public, given that these fossils actually belong to the public,” though they are kept in the care of museums,.
With almost 1,700 bones excavated during the past three years, scientists have about 90 percent of Falcarius’ bones and believe the skeletal remains show several signs of this major evolutionary transition.
It had leaf-shaped teeth designed for shredding plants rather than the triangular, blade-like serrated teeth of its meat-eating relatives. Its pelvis was broader, indicating a larger gut to digest plant material, which is more difficult to process than meat. Its lower legs were stubby, presumably because it no longer needed to run after prey. Compared with carnivorous relatives, Falcarius’ neck was more elongated and its forelimbs were more flexible, perhaps for reaching plants to eat.
“Falcarius represents evolution caught in the act, a primitive form that shares much in common with its carnivorous kin,” Sampson said, while possessing features showing it had embarked on a path toward plant-eating forms.
Sampson said the rise of plant-eating therizinosaurs “may have been directly linked to the spread of flowering plants about 125 million years ago.”
Falcarius means sickle-maker, so named because later plant-eating therizinosaurs had 3-foot-long, sickle-like claws. The species name,
utahensis, comes from the fact the new species was discovered in east-central Utah.
The new species was excavated from ancient gravelly mudstones at the base of the Cedar Mountain rock formation, at a site named the Crystal Geyser Quarry after a nearby manmade geyser that spews cold water and carbon dioxide gas.
Hundreds or thousands of dinosaurs, from hatchlings to adults, died at the 2-acre dig site, Kirkland estimates. There are a number of such mass deaths in the fossil records, Sampson said, and have been attributed to causes including drought, volcanism, fire and botulism poisoning from carcass-tainted water.
Kirkland leans toward a theory developed by Celina and Marina Suarez, twins who are geology graduate students at Temple University in Philadelphia. They have proposed the area was near
or in a spring, and that there were at least two mass die-offs. The spring might have repeatedly attracted dinosaurs with water or nearby food, such as plants growing by it, and then occasinonally poisoned the reptiles with toxic gas or water, Kirkland said.
Therizinosaurs have been found for 50 years in China and Mongolia, but were not recognized as a distinct group until about 25 years ago, Sampson said. The only therizinosaur known previously from North America was
Nothronychus, which Kirkland discovered in the late 1990s in New Mexico. It was 90 million years old, so scientists initially believed the older therizinosaurs in China had migrated over a land bridge from Asia through Alaska to the American Southwest.
But due to the constantly shifting plates of Earth’s surface, Alaska didn’t exist 125 million years ago – the age of both Falcarius and the oldest known Chinese
therizinosaur, Beipiaosaurus. So scientists now wonder if therizinosaurs originated in Asia and migrated through Europe to North America while the continents were still attached, or if they originated in North America and migrated in the opposite direction.
“This discovery,” Zanno said, “tells us that North America potentially could be the place of origin for this group of dinosaurs.”
Kirkland said Falcarius likely was covered with shaggy, hair-like “proto-feathers,” which may or may not have had a shaft like those found in bird feathers.
No feathers were found with the Falcarius fossils. Feathers rarely are preserved, but “a number of its close relatives found in China had feathers [preserved by unusual lake sediments], so the presumption is this animal too was feathered,” Sampson said.
Therizinosaurs have been enigmatic. Until Falcarius, only “bits and pieces” of other species’ skeletons had been found, and “their anatomy was so different from that of any other dinosaur that we didn’t know what to make of them,” Zanno said.
The most recent therizinosaurs – which lived 94 million to 65 million years ago – had larger bodies, long necks, short legs, broad hips, short tails, lightly built skeletons, small heads and many small, leaf-shaped teeth – except at the front of the face where there likely was a beak and – in the case of Therizinosaurus – 3-foot-long claws.
The plant-eating, elephant-sized Therizinosaurus – a name that means sickle lizard – was “the ultimate in bizarre,” resembling “a cross between an ostrich, a gorilla and Edward
Scissorhands,” Zanno said.
Kirkland said it is not surprising that Falcarius represents an intermediate step between carnivorous and herbivorous dinosaurs because “all lines of plant-eating animals had meat-eating ancestors.” Long before
Falcarius, many plant-eating dinosaurs already had arisen from meat-eating relatives, he added.