A few years
ago, Utah State Paleontologist James Kirkland saw an unusual specimen for sale
at a fossil and gem show. Months later, he finally reached the person who had
collected the fossil and took a trip to the collection site.
A new dinosaur, called Falcarius utahensis,
has provided a previously missing link between carnivorous and herbivorous therizinosaurs,
which lived millions of years apart. Researchers working on this odd-looking
creature have described it as a cross between an ostrich, a gorilla and Edward
Scissorhands. Image copyright by Mike Skrepnick.
Although the fossil collection and sale were illegal, paleontologists
are excited about the site: It contains hundreds of individuals of a new type
of dinosaur, named Falcarius utahensis, that is helping bridge the evolutionary
gap between a type of dinosaur that started out carnivorous but eventually turned
herbivorous.
The new creature lived about 125 million years ago and was part of a “bizarre-looking”
group of dinosaurs called therizinosaurs, says Scott Sampson, curator of the
Utah Museum of Natural History and a paleontologist at the University of Utah.
An adult Falcarius walked on two legs, was about 4 meters long and 1.4
meters tall at the hip, had 10-centimeter-long sharp, curved claws and was likely
covered in feathers, Kirkland, Sampson and colleagues reported in the May 5
Nature. The dinosaur had leaf-shaped “shredding” teeth that
could have chomped both vegetation and small-bodied animals, and fairly broad
hips that indicate a “big gut,” which is a characteristic of plant-eaters,
Sampson says. “It’s very likely that Falcarius was an omnivore,”
he says.
Since their discovery, scientists have tried to figure out where these odd creatures
fit in the dinosaur family tree. Although most known therizinosaurs were strict
vegetarians, scientists have placed them in the largely carnivorous theropod
grouping, which includes velociraptors and modern birds, says Lindsay Zanno,
a doctoral student at the University of Utah who studies therizinosaurs and
is a co-author of the study. Scientists think that somewhere down the line,
raptor-like carnivorous therizinosaurs evolved into herbivores, she says.
Younger therizinosaurs all show “very clear herbivorous variations,”
says Thomas Holtz, a paleontologist at the University of Maryland, including
shredding teeth, shorter, stockier legs (“they didn’t have to run
very far or fast to chase after plants”), longer necks and smaller heads.
By contrast, older species, which were meat-eaters, have longer legs to run
faster, smaller skeletons, predatory claws, and long, dexterous arms and hands
good for grabbing prey, Zanno says. “Falcarius is a mix,” Holtz
says. “It is the no-longer-missing link.”
“Falcarius is the most primitive member of this bizarre group and
links therizinosaurs to more regular predatory dinosaurs,” says Larry Witmer,
a paleontologist at Ohio University. The specimen shows vestiges of the “big
nasty claws” common to predators, but its hips, belly and legs “document
the transition between meat-eating and plant-eating dinosaurs,” he says.
This important discovery helps piece together the genealogical history of the
big-game dinosaurs, he says, and also helps to place therizinosaurs in the right
branch on the dinosaur family tree.
Another important aspect, Holtz says, is that until this find, most of what
had been known about therizinosaurs came from single individuals. This is the
first time scientists have found a bone bed with multiple individuals, he says,
which could help answer questions about how the creatures grew and developed,
and how they lived and raised their young. “It’s an exciting find,”
Holtz says.
About a dozen Falcarius individuals have been unearthed, but the site
likely contains hundreds, Sampson says. Why these animals died here remains
a mystery, he says, but the leading scenarios involve either poisoning from
a water source or drought, during which animals have been known to gather around
water holes and eat everything in sight, only to die eventually of starvation.
The cause of death may never be determined, he says.
Scientists will not excavate the entire 2-acre site — it’s just too
big, Sampson says, and they want to leave something behind for future excavations.
Future studies, Zanno says, will focus on understanding the evolutionary family
tree of maniraptorans, of which the therizinosaurs are a part, and “reconstructing
what Falcarius’ lifestyle was like to see how and why these creatures
became so bizarre.”
Megan Sever
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