Newly discovered dinosaur reveals fearsome 'switchblade' claw
Trauma to the extended talon helped researchers determine that it was used for attacking, not to help the dinosaur maintain its balance.
Tue, Sep 20 2011 at 9:54 AM
Battle damage linked to the fearsome curving talon of a newly discovered dinosaur relative of Velociraptor is shedding light on how it was used as a weapon, scientists find.
This research also adds to the mysterious complexity seen in the lost continent where this fossil was found, researchers added.
The newfound 75-million-year-old dinosaur is a feathered raptor named Talos sampsoni — "Talos" in homage to a winged bronze giant in Greek mythology that could run at lightning speed and that succumbed to a wound to his ankle, "sampsoni" in honor of Scott Sampson of the PBS series "Dinosaur Train," and a research curator at the Utah Museum of Natural History.
The raptor dinosaurs, made famous by the book and film "Jurassic Park," all possessed unusually large, sickle-like claws on the second toes of each foot, which they held off the ground like folded switchblades.
A famous discovery made in Mongolia 30 years ago seemingly of a Velociraptor locked in mortal combat with prey — fossils dubbed the "fighting dinosaurs" — suggested these talons were used as weapons. Now the injured claw of Talos sheds even more light on how they lived with these weapons.
Talos was a type of troodontid, a group of dinosaurs whose anatomy suggests they were closely related to birds. [See Avian Ancestors: Dinosaurs That Learned to Fly]
Estimated to have been about 6 feet (2 meters) long and weigh about 83 pounds (38 kilograms), Talos was neither the smallest nor largest troodontid. For instance, Talos was much larger than tiny troondontids such as Anchiornis, which may have been as small as 100 grams, while it was smaller and more slender than its approximately 8-foot-long cousin Troodon, after which this group of dinosaurs is named. "Talos was fleet-footed and lightly built," said researcher Lindsay Zanno, a vertebrate paleontologist at the University of Wisconsin-Parkside. "This little guy was a scrapper." (Zanno is also a research associate at the Field Museum of Natural History in Chicago.)
The researchers discovered the specimen in the 1.9-million-acre Grand Staircase Escalante National Monument in southern Utah. The area is one of the last pristine dinosaur graveyards in the United States, with at least 15 new dinosaur species discovered there in just the past decade, including the turkey-like Hagryphus giganteus, horned dinosaurs Kosmoceratops and Utahceratops, duck-billed dinosaurs, including Gryposaurus monumentensis, two new tyrannosaurs and a number of armored dinosaurs known as ankylosaurs.
"Finding a decent specimen of this type of dinosaur in North America is like a lighting strike," Zanno said, referring to the fact that troodontids are known nearly exclusively from Asia. "It's a random event of thrilling proportions."
Researcher Michael Knell also voiced his excitement: "I was surprised when I learned that I had found a new dinosaur," said Knell, a doctoral student at Montana State University. "It is a rare discovery, and I feel very lucky to be part of the exciting research happening here in the monument." He stumbled across the remains of Talos while exploring the area for fossil turtles as part of his doctoral research.
After the researchers began studying the fossil, they discovered what appeared to be signs of trauma to its second toe on its left foot, the one that would have bore an enlarged hook-like claw.
"When we realized we had evidence of an injury, the excitement was palpable," Zanno said. "An injured specimen has a story to tell."
Evidence of injury can shed light on how a body part was used, the researchers explained. An injury to the foot of a raptor dinosaur, for example, can yield new details about the potential function of its toes and claws.
"Normally we think that the most pristine fossils we can find perhaps yield the most important information, but in fact sometimes it's the beat-up, damaged, injured specimens that can give you clues about the biology of an extinct animal you wouldn't have otherwise," Zanno told LiveScience. [Image Gallery: Dinosaur Fossils]
Using a high-resolution micro-CT scanner, Zanno and her colleagues saw the injury was restricted to the toe with the enlarged claw — it had either been fractured or bitten and then suffered from a localized infection.
"People have speculated that the talon on the foot of raptor dinosaurs was used to capture prey, fight with other members of the same species, or defend the animal against attack," Zanno said. "Our interpretation supports the idea that these animals regularly put this toe in harm's way."
Intriguingly, the injured toe showed signs of the kind of changes in bone that occur over many weeks to months, suggesting that Talos lived with a serious injury to its foot for a long time.
"Whatever it typically did with the enlarged talon on the left foot, whether that be acquire prey or interact with other members of the species, it must have been capable of doing so fairly well with the one on the right foot," said researcher Patrick O'Connor at Ohio University.
Footprints made by raptors closely related to Talos suggest they all held the switchblade talon off the ground when walking.
"Our data support the idea that the talon of raptor dinosaurs was not used for purposes as mundane as walking," Zanno said. "It was an instrument meant for inflicting damage."
It remains uncertain what Talos might have eaten. "Many are still debating over what its relatives ate," Zanno said. "My recent research suggests it was probably either a carnivore or an omnivore, eating some degree of prey."
Talos lived in a warm greenhouse world devoid of polar ice caps. In what is now North America, a shallow seaway that ran from the Gulf of Mexico through to the Arctic Ocean divided the continent into two landmasses, East America, or Appalachia, and West America, or Laramidia, for several million years.
"The area was basically the complete antithesis of what it is now," Zanno said. While the area is now quite dry, "it was extremely wet then, a very, very lush environment, almost swampy, and regularly bombarded by massive storms coming in off the seaway that divided North America at the time."
Mysteriously, the dinosaurs of the lost continent of Laramidia appeared to be unusually diverse. Normally, large animals are expected to span the whole area in which they live, as is the case with coyotes and mountain lions nowadays, and this might be expected to prove true with relatively small continents such as Laramidia. However, dinosaurs from the rock formation holding Talos are entirely distinct from ones living just a few hundred miles to the north in what is now Montana and Alberta.
"We already knew that some of the dinosaurs inhabiting southern Utah during the Late Cretaceous were unique, but Talos tells us that the singularity of this ecosystem was not just restricted to one or two species — rather, the whole area was like a lost world in and of itself," Zanno said.
When it comes to how this diversity might have developed, "we're just asking that question now," Zanno added. "Some preliminary research done by a colleague of mine suggests there may have been geographic barriers — mountain ranges and rivers — dividing up populations, keeping them isolated for long enough to become new species."
Much could still be found in this region. "We're going to continue scouring these badlands — this area is one of the last dinosaur graveyards anywhere in the United States," Zanno said.
The bones of Talos will be on exhibit for the first time in the Past Worlds Observatory at the new Utah Museum of Natural History in Salt Lake City. The scientists detailed their findings online Monday in the journal PLoS ONE.
Image: Jorge Gonzales/Utah Museum of Natural History
This article was reprinted with permission from LiveScience.
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