Fossil hunter unearths half-grown T. rex

A Kansas fossil hunter has unearthed the remains of what is believed to be a half-grown Tyrannosaurus rex from Montana that could help fill a void in paleontologists' understanding of the king of the dinosaurs.

This Oct. 29 photo provided by Robert Detrich is an ischium, the back lower part of the hip bone from what is believed to be a half-grown Tyrannosaurus rex in Lusk, Wyo. Detrich, of Wichita, unearthed the fossil dubbed "Baby Bob" in a fossil-rich area in eastern Montana. The find is generating excitement because if all the preliminary data pans out, it would be among the smallest T. rex specimens ever found [Credit: AP/Todd Hoelmer]

Robert Detrich, of Wichita, Kan., unearthed the fossil dubbed "Baby Bob" in July in a fossil-rich area near the eastern Montana town of Jordan. It's generating excitement because its femur measures about 25 inches, and if all the preliminary data pans out, that would make it among the smallest T. rex specimens ever found.

"This is the discovery everyone wishes and longs for," Detrich said.

Detrich has been sharing his findings with other researchers, including the Smithsonian Institution. Scientists are eager to learn more about the years before the carnivore reached its terrifying full size of about 40 feet from head to toe. Detrich estimates that Baby Bob was about half that size.

"We hardly know anything about how T. rex grew up," said Thomas Carr, director of the Carthage Institute of Paleontology at Carthage College in Kenosha, Wis. "We really only have a handful of fossils of sub-adults and juveniles, so any additional fossils that can fill in that early end of the growth period is scientifically very important because most of the skeletons of rex that we have are from adults."

Bob Bakker, curator of paleontology at the Houston Museum of Natural Science, said the scarcity of half-grown T. rex fossils has raised questions. Could it be, he asked, that young T. rex stayed in the nest until they were almost full grown?

"If this is a really good genuine baby T. rex, it could tell us whether it was fit to hunt on its own or whether it looks like it was designed to wait for mom and dad to come back," Bakker said

Another juvenile fossil also could help settle a debate about whether the T. rex has a smaller cousin, called the nanotyrannus, or nano for short. Bakker is among those certain there are two species, while Carr is part of another group that believes suspected nano fossils are actually juvenile T. rex remains. Another juvenile T. rex would give scientists something to use for comparison purposes.

Baby Bob has been fully excavated, although it will take another year to clean. Detrich said the skull, which is about 75 percent complete, and most of the major skeletal elements were found strewn across a flood plain, although very few vertebra and ribs were found.

"This is so exciting," Detrich said. "I can't even tell you the importance of this dinosaur."

As a commercial fossil hunter, Detrich eventually plans to sell the fossil. He said most of his fossil finds have found homes in museums. He's hopeful the same would happen to Baby Bob.

Carr, also an associate professor of biology, said the fossil will be of little use scientifically if that doesn't happen. He said that a nearly complete T. rex named Samson that Robert and his brother, Alan, were involved in excavating two decades ago in South Dakota wound up in private hands.

"If this skeleton ends up in private hands," Carr said of Baby Bob, "it is taken away from science and science loses."