The secret's out: JANE's a juvenile Tyrannosaurus rex

StoryImage( ‘/Images/Story//Auto-img-11200684418638.jpg’, ”, ‘Burpee Museum Curator of Earth Sciences, Michael Henderson (left) works with volunteer Richard Hertzing (right) to remove the rocky matrix from JANE's bones.’);

After nearly three years of intensive examination, a team of paleontologists led by Burpee Museum of Natural History’s Curator of Earth Sciences Michael Henderson has determined that the small tyrannosaurid dinosaur nicknamed “JANE” is a juvenile Tyrannosaurus rex.

“What we have is an animal that died at an important stage in its life cycle—just before a dramatic growth spurt would have transformed it into the massive adult animal that we know as T. rex,” says Henderson.

Prior to Burpee Museum’s discovery of JANE in 2001, paleontologists had long debated the existence of a species of “pygmy tyrannosaur” called Nanotyrannus lancensis. The identity of this small cousin to T. rex was based solely on loose teeth and a single skull collected in Montana by the Cleveland Museum of Natural History.

Some paleontologists interpreted these fossils as belonging to a full-grown adult of a small species of tyrannosaur, which was eventually dubbed Nanotyrannus. Others argued that they represented juvenile specimens of Tyrannosaurus rex. With such scant evidence to support either claim, the controversy continued for more than 40 years.

JANE appears on the scene

In 2001, a group of staff and volunteers from Burpee Museum, a small natural history museum in Rockford, traveled to southeastern Montana to prospect for fossils. During the trip, two volunteer fossil hunters happened upon a couple of foot bones weathering out of the side of a hill. It soon became clear that the bones were from a tyrannosaurid dinosaur, but they were far too small to belong to an adult T. rex. Did they belong to a Nanotyrannus?

After excavating the rest of the skeleton (by now nicknamed “JANE” in honor of a museum benefactor) and bringing it back to Burpee Museum, Henderson, whose expertise is fossil invertebrates, assembled a team of the world’s leading dinosaur paleontologists to assist him in determining JANE’s identity.

“We started making phone calls to find out who might be willing to help us. To our surprise, as word about JANE spread throughout the paleontological community, the experts started calling us, asking if they could help,” says Henderson.

Tooth count and growth rings

Over the next three years, as fossil preparators carefully extracted each of JANE’s 145-plus bones from their field jackets, Henderson examined them and compared them to the bones of tyrannosaur specimens held in museums across North America.

Initially, it seemed that JANE’s skeleton had a number of features that looked different from those of an adult T. rex. But as Henderson surveyed juvenile tyrannosaurid dinosaurs at other museums, he discovered that they had many of these same features.

One of the features that initially set JANE apart from T. rex is what scientists call “tooth count.” With a total of 72 teeth, JANE has 12 more than the typical adult T. rex. However, after examining dozens of dinosaur jaws and discussing his findings with his colleagues, Henderson became convinced that T. rex lost teeth as it reached adulthood.

And, of course, there was JANE’s diminutive size. Just half the size of an adult T. rex, JANE could either be a full-grown small dinosaur or a half-grown big dinosaur.

Then, one day, Henderson received an unexpected visit from Dr. Greg Erickson, a paleobiologist from Florida State University. Erickson had discovered a way to count growth rings inside of dinosaur bones to tell how old they were when they died. Henderson supplied him with a piece of JANE’s shinbone and, within a few months, Erickson had determined that, at the time of death, JANE was 11 years old—and still growing.

In the end, all the evidence pointed to the same conclusion: Rather than being an adult Nanotyrannus, JANE is a juvenile T. rex. So what does this mean for Nanotyrannus?

“Nanotyrannus is no more, basically,” says Henderson. “When we first laid eyes on JANE, we thought for sure we had a Nanotyrannus. But a closer examination has changed our minds. That’s the way science works. You have to go with what the bones tell you. JANE told us she’s a young Tyrannosaurus rex. And that’s just fine with us.”

From the June 29-July 5, 2005, issue

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