Paleontologists from the Utah
Geological Survey and the Utah Museum of Natural History announced the
discovery of a bizarre new species, Falcarius utahensis, in the May 5, 2005,.
issue of Nature Magazine. James Kirkland, Utah state
paleontologist at the Utah Geological Survey and principal scientist
for the new study. He said, "This little beast is a missing link
between small-bodied predatory dinosaurs and the highly specialized
and bizarre plant-eating therizinosaurs."
The new species was excavated from ancient gravely 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. It was discovered in a mass graveyard
containing hundreds, if not thousands, of individuals, including
everything from hatchlings to adults. The was discovered by a
commercial 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 says. "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
Scientists have suggested a number of possible explanations for
such mass deaths. Scott Sampson, chief curator at the Utah Museum of
Natural History and an associate professor of geology and geophysics
at the University of Utah. Sampson says that they include drought,
volcanism, fire and botulism poisoning from water tainted by
carcasses. Kirkland leans toward a theory developed by Celina and Marina
Suarez, twins who are geology graduate students at Temple University
in Philadelphia. Their research on carbonate-rich sediments in which the dinosaurs
were buried suggests the area was near or in a spring, and that there
were at least two mass die-offs. That raises the possibility the dinosaurs were drawn repeatedly to
the site by water or an attractive food source – perhaps plants
growing around the spring – and then the spring occasionally would
poison the animals with toxic gas or water, Kirkland says.
With almost 1,700
bones excavated during the past three years, scientists have about
90 percent of Falcarius' bones, making it the most complete
therizinosaurus specimen found to date. Falcarius "is the most primitive known therizinosaur, demonstrating
unequivocally that this large-bodied group of bizarre herbivorous
group of dinosaurs came from Velociraptor-like ancestors," says study
co-author Lindsay Zanno, a graduate student in geology and geophysics
at the University of Utah and the Utah Museum of Natural History.
Sampson maintains that Falcarius did not descend directly from
Velociraptor, but both had a common, yet-undiscovered ancestor, says
study co-author and paleontologist
Kirkland says 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 says.
The previously unknown species provides clues
about how vicious meat-eaters related to Velociraptor ultimately
evolved into plant-munching vegetarians. The adult dinosaur walked on two legs and was about 13 feet long (4
meters) and stood 4.5 feet tall (1.4 meters). It had sharp, curved,
4-inch-long (10 centimeter) claws.
Scientists do not yet know if the creature ate meat,
plants or both. Kirkland said, "Falcarius
shows the beginning of features we associate with plant-eating
dinosaurs, including a reduction in size of meat-cutting teeth to
leaf-shredding teeth, the expansion of the gut to a size needed to
ferment plants, and the early stages of changing the legs so they
could carry a bulky body instead of running fast after prey."
Falcarius, which dates to the Early Cretaceous Period
about 125 million years ago, belongs to a group of dinosaurs known as
therizinosaurs. Falcarius and Beipiaosaurus are about the same age and
appear to represent an intermediate stage between deadly carnivores
and later, plant-eating therizinosaurs. Falcarius is anatomically more
primitive than the Chinese therizinosaurs.
Falcarius 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. Sampson says: "Falcarius
represents evolution caught in the act, a primitive form that shares
much in common with its carnivorous kin, while possessing a variety of
features demonstrating that it had embarked on the path toward more
advanced plant-eating forms."
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, south of the town of Green River.
Falcarius is the fourth new dinosaur species Kirkland has discovered
in the Cedar Mountain Formation's Yellow Cat member (a unit of the
formation) in 11 years. Others are meat-eaters Utahraptor and
Nedcolbertia, and an armored dinosaur named Gastonia.
"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 says. 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 before the Atlantic Ocean basin opened up, or
if they originated in North America and migrated through Europe to
Asia. "Falcarius may have been home-grown," Kirkland says."
discovery puts the most primitive therizinosaurs in North America,"
Zanno says. "This tells us that North America potentially could be the
place of origin for this group of dinosaurs."