To paleontologists, the news was only slightly less startling than if someone had spotted a live Apatosaurus stomping around the bayous of Louisiana. Last March Mary Schweitzer of North Carolina State University reported that she had extracted soft tissue from the 68-million-year-old fossilized femur of a Tyrannosaurus rex. Her finding, if confirmed, overthrows every grade school textbook’s explanation that fossils result from the mineralization of bone and the destruction of soft tissue. It also opens staggering possibilities. If tissue proteins can survive for millions of years, scientists could analyze them to make detailed interpretations of the biology of ancient species and their relationship to those living today.
The discovery happened after Schweitzer and a lab technician, Jennifer Wittmeyer, had soaked some T. rex bone in a solution so they could cut it into slices. “She came running in and said, ‘You’re not going to believe what has happened!’ ” Schweitzer recalls. “She went to pick up a chunk of bone we had demineralized, and it was stretchy. A few weeks later, we set up the experiment as before, and it happened again. We have a little movie of our tweezers stretching the material. You can see the blood vessels flexing inside.”
Schweitzer soon extracted similar stretchy vessels from two other tyrannosaurs and found hints of preserved bone cells in a duck-billed dinosaur. She is now analyzing the soft material to determine its composition and, above all, to see if it contains intact biological molecules. She is also trying to figure out how the T. rex fossil, unearthed from the Hell Creek Formation in Montana, could have retained a semblance of its original texture and chemistry. “We’ve got to get out into the field to figure out if there is something in this environment that might give us that information,” she says.
Three months after her first paper appeared, Schweitzer published another stunner. This time she announced that calcium-rich bone tissue in the same specimen resembles equivalent tissue in birds that are producing eggs. She concluded that this T. rex had been an actively reproducing female and that dinosaur biology mirrored bird biology in a crucial way. The argument that birds evolved from feathered dinosaurs suddenly got another plume in its cap.
To some researchers this all sounds too good to be true. “Give me a break,” says Alan Feduccia, a biologist at nearby University of North Carolina in Chapel Hill and a leading skeptic of the bird-dinosaur connection. He rejects both the soft-tissue discovery and the interpretation of the calcified bones. Schweitzer’s claims are, he worries, an example of the paleontology “arm waving” that finds its way into respectable journals. “These papers get published in Science or Nature, but they are really just announcements,” Feduccia says. “They don’t have detail, and then there’s no follow-up.”
Over at the Field Museum in Chicago, T. rex expert Peter Makovicky differs with Feduccia on many points but agrees on the need for caution. “How you get something buried for nearly 70 million years and not be altered is the $64,000 question,” he says. “The trick to all science is reproducibility, and that’s what we’re waiting for. At the same time we have to be open minded. Fifteen years ago, no one would have predicted we’d have 10 or 12 species of feathered dinosaurs or so many nesting individuals or embryos.”
Schweitzer admits that she “absolutely freaked out” when she first recognized the implications of her discoveries. Now she is examining more bones and searching for intact proteins or collagen. She expects to have some of those follow-up answers by the end of the year and hopes for another result worthy of a freak-out: “What if we can find a real dinosaur molecule?”
THE SURPRISING S CURVE OF RAPID DINOSAUR GROWTH
In recent years, fossils have yielded amazing new information about ancient animals, including brain morphology, heart structure, and stages of embryonic development. Recently, analysis of growth lines in fossil bones, most notably by Gregory Erickson of Florida State University, has yielded ages of dinosaur specimens as well as their maturation rates. Shown here are three archetypal dinosaurs (left column) and a modern bird, mammal, and fish (right column).
MAIASAURA A fast-growing duckbill,
it may have guarded nests of its young.
|OSTRICH Birds generally have higher maximal growth rates than dinosaurs.|
TYRANNOSAURUS This predator outgrew its relatives during a teen growth spurt.
HUMAN A person takes 20 years to reach full size, as long as a giant Apatosaurus.
|APATOSAURUS It ate enough plants to add 10,000 pounds per year in adolescence.||WHITE SHARK Its life history is nearly as poorly documented as that of dinosaurs|
A SERIES OF TIMELY AND LUCKY EVENTS
MARY SCHWEITZER of North Carolina State University recently rocked the world of dinosaur research with twin discoveries: preserved soft vascular features in a Tyrannosaurus rex fossil and bone tissue indicating that the animal was about to lay eggs.
Was there a eureka moment?
S: Which eureka moment would you like? We received these bone fragments from the interior part of a T. rex femur that Jack Horner [of the Museum of the Rockies] had had to break to remove from the field. I pulled out a fragment, took one look at this bone chunk, and said, “Oh, my gosh, we have a female dinosaur, and she’s pregnant.”
How did you know that?
S: It had bone tissue on the internal surface unlike anything we’ve ever seen before. I have done a lot of research on dinosaur-bird physiology, and I have learned a lot about bird reproduction. When a bird shells, it typically has to mobilize as much calcium in 24 hours as a woman does when she’s been pregnant and nursing for 18 months. So birds have developed the medullary bone, a buffer to the calcium draw on their bones. Medullary bones have characteristics not shared by other bone types. The minute I saw the bone fragment, I knew what it was.
Was it just luck that you got a sample from a T. rex that was about to lay eggs?
S: When you think about a T. rex getting pregnant and then dying while producing eggs and then getting fossilized and then being found by a paleontologist—that conjunction of events is extremely rare, although that’s not to say that it wouldn’t happen again. One of the cool things about this kind of research is that it allows us to make some predictions. And one of those is, if dinosaurs were like birds and if you could find dinosaurs with eggs in their reproductive tract, they should also have medullary tissue in their bones. If the dinosaur were brooding, that tissue would no longer be present.
How are you going to test that prediction about dinosaur reproduction?
S: We can look at the dinosaur reported just a few months ago in Science by Tamaki Sato [of the Canadian Museum of Nature]. She says she has an oviraptor fossil with two eggs inside the body cavity. And Mark Norell [of the American Museum of Natural History] and a few others have found dinosaurs that were fossilized alongside their brood.
What happens now? Will you go ahead and test to see whether dinosaurs produced eggs the same way birds do?
S: I’m trying. Most people don’t like to do destructive analysis on their fossils. The American Museum of Natural History probably won’t allow us to do the study. I’m still trying to negotiate with Sato.
Will we be able to find dinosaur DNA?
S: If you had asked me that question a year ago, I would have said absolutely not. Now I never say never. Everyone knew that soft tissues don’t last more than a month, but we’ve got them in a T. rex. The problem with isolating ancient DNA is that there is such a risk of contamination. I do think, though, that you can get almost as much phylogenetic information out of a strand of protein—and finding that is not impossible.
I have to ask the Michael Crichton question. But please don’t make me say it.
S: OK. No, we will never clone a dinosaur.