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Tiny Tyrant—Fossil May Be Mini T. Rex Cousin

By Bijal P. Trivedi
National Geographic Today
August 9, 2002
 
Paleontologists from a small museum in Rockford, Illinois, have found what they believe to be the skeleton of the tiny tyrant Nanotyrannus—a smaller, faster but equally ferocious meat-eating relative of Tyrannosaurus rex.

The only known evidence of this dinosaur is a single specimen, a skull, which resides in the Cleveland Museum of Natural History. But the Cleveland skull has been the focus of controversy; some believe it is Nanotyrannus, a new genus of dinosaur, while others claim it is a juvenile T. rex, which has never been found.

"I'm 100 percent sure that what we have here is Nanotyrannus," said Michael Henderson, curator of Earth Science at the Burpee Museum of Natural History in Rockford. "When we saw the teeth we knew exactly what we had."

Based on the skull and a collection of teeth gathered from Montana, South Dakota, and Wyoming, Henderson and his colleagues believe that the teeth of Nanotyrannus are slim and razor-like for slicing through flesh. T. rex, by contrast, has teeth like railroad spikes—larger and rounder for piercing and puncturing prey and biting through bones.



Furthermore, the new specimen is definitely not a juvenile, said Henderson, who led the expedition into the southeastern corner of Montana where the dinosaur was discovered. "It has a couple of fused vertebrae and the three pelvic bones are fused into one bone, which would only occur in an adult," he said.

The specimen, named "Jane" for a major donor to the Burpee Museum, is thought to have lived sometime between 68 and 65 million years ago—just before the mass extinction that wiped out the dinosaurs. She looks about 22 feet long and her long, narrow shin and anklebones suggest that she was "the cheetah of the Cretaceous," said Robert Bakker, who first described Nanotyrannus in 1988 together with co-authors Phil Currie and Mike Williams.

Discovery by Amateurs

Jane was actually discovered in June 2001 by volunteer dinosaur hunters Bill Harrison and Carol Tuck while on a prospecting expedition led by Henderson in Montana's Badlands.

They discovered a six-inch-long toe jutting out of the base of a 20-foot (6-meter) cliff face. From here they noticed a cross section of a lower limb, and lower down, a foot and pelvis, which implied that there was a significant portion of the skeleton within the cliff.

Henderson marked the site, removed the toe and foot bone, and returned nearly one year later in May 2002 with permits, shovels, and volunteers.

"Until about two weeks ago we had no idea what we had found," said Joe Peterson, a junior at Southern Illinois University at Carbondale and an assistant to Henderson. A broken bone with a hollow space inside indicated that the creature was a carnivore, but yielded few other clues. When the toe was compared to specimens at the Black Hills Museum of Natural History in Hill City, South Dakota, last year, the team suspected that they had found Struthiomimus, an ostrich-like carnivorous dinosaur from the late Cretaceous period that was a tremendously fast runner.

But as soon as the groups began to excavate and the lower jaw became visible, Henderson said, "we knew" it was Nanotyrannus.

At present most of the skeleton remains embedded in an enormous slab of rock that was loaded on a truck and is expected to arrive back in Illinois.

150-Year Mystery

Henderson has removed enough sediment to reveal between 80 and 90 bones in the stone slab. Based on an adult T. rex skeleton he believes he has at least one-third of the full skeleton, including major bones—half the tail, ribs, vertebrae, the upper arm, the lower jaw with teeth, foot, leg, and skull.

"This is one of the great finds of the century," said Peter Larson, director of the Black Hills Institute of Geological Research, Inc., in Rapid City, South Dakota. Larson gained notoriety after his discovery of "Sue," the largest and most well preserved T. rex fossil found to date. "Even the bones that are used to determine the sex of the dinosaur are present," he added.

"I feel like I've won the lottery. People have been looking for this for a very long time," Henderson said.

"This dinosaur has been a mystery for more than 150 years," said Bakker. "A tooth was found in the 1880s, a leg around 1900, a skull in the 1940s, and just a few years ago more teeth. This thing has been a huge mystery."

Henderson's excitement was buoyed by the fact that such extensive finds in the Hell Creek Formation of Montana are rare. The reason: The band of sediment where Jane was buried was from a floodplain where gushing waters 65 million years ago dispersed the bones of dead dinosaurs before they could be encapsulated and buried under protective sediments.

Juvenile T. rex?

Thomas Carr, a graduate student at the University of Toronto now completing his dissertation, disputes whether Nanotyrannus exists.

Using an analysis of growth changes seen in the skull of a well-known Tyrannosaurid called Albertosaurus for comparison, Carr reasoned that the Cleveland skull belonged to a juvenile T. rex. His research, a master's thesis, was published as the cover story in the September 1999 issue of the Journal of Vertebrate Paleontology.

The narrow snout, wide braincase, and skull growth patterns all suggested to Carr that the Cleveland skull belonged to a juvenile.

People seem to be very dismissive of the fact that this could be a juvenile T. rex, said Carr. "This is the only window on the growth and development of the most famous dinosaur in history—it is worth its weight in gold."

At least one year of work remains before the bones are released from the stone bonds. Only then will scientists really be able to assess whether this is truly a new genus.

"The significance of this find is really that we expect this specimen to give us the answer and settle the debate," said Henderson. "But if this turns out to be a juvenile T. rex, then we will know that the youngster was quite different to the adult."

Recent National Geographic News stories on dinosaurs:
New Find: Pterosaur Had Strange Crest, Fishing Style
Fossil of Dog-Size Horned Dinosaur Unearthed in China
Tyrannosaurus rex Was a Slowpoke
Researchers Rethink Dinosaur Die Off Scenario
Researchers Melt Polar Dinosaur Mysteries
Scientist's Finds Spur New Thinking on Dino Evolution
Dino-Era Vomit Fossil Found in England
Study Paints New Picture of Dinosaur's Nose
Skeleton of New Dinosaur "Titan" Found in Madagascar
"Tidal Giant" Roamed Coastal Swamps of Ancient Africa
"Feathered" Fossil Bolsters Changing Image of Dinosaurs
Oddly Angled Teeth Make Masiakasaurus Stick Out

Additional dinosaur resources from National Geographic:
Paul Sereno: National Geographic Explorer-in-Residence and Dinosaur Hunter
Dinorama
Wanted: Albertosaurus
Dinosaur Eggs
Destinations: Dinosaur National Monument

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