Soft-tissue discovery opens a biochemical frontier for paleontologists
By Alan Boyle
ST. LOUIS – Someday, biochemists will be able to figure out what dinosaurs ate, what diseases afflicted them and how they were related to each other — all by analyzing a bit of organic goo.
At least those are the kinds of tests that could theoretically be carried out in a new field dubbed "paleoproteomics." Paleontologists are becoming increasingly intrigued by the possibilities in the wake of last year’s discovery that some of a Tyrannosaurus rex’s soft tissues — perhaps its blood cells, blood vessels or fibrous cells — could survive the process of fossilization intact.
No one is saying yet that the DNA of a dinosaur could be reconstructed, as it was in the fictional "Jurassic Park" movies. DNA molecules are made up of long chains that degrade over time. Under the best circumstances, it’s hard for DNA to survive thousands of years, let alone millions. It’s more likely that shorter-chain protein molecules could be recovered from the soft tissues. But even those molecules could tell a lot about how dinosaurs lived.
"Molecules are fossils, too," Michigan State University zoologist Peggy Ostrom said Thursday at the annual meeting of the American Association for the Advancement of Science, conducted in St. Louis.
Ostrom and the researcher behind the soft-tissue discovery, Mary Higby Schweitzer of North Carolina State University and the North Carolina Museum of Natural Sciences, discussed how protein-based biochemistry could revolutionize the study of long-gone species.
The two researchers are coming at the issue from different directions: Ostrom has been working to analyze the proteins found in bones of animals that lived tens of thousands or even hundreds of thousands of years ago. Most recently, she and her colleagues were able to extract a protein sequence from the bones of a 500,000-year-old musk ox.
"Protein sequences may very well last longer than DNA," she told MSNBC.com.
She said those protein sequences could confirm the organic signature of a particular species, provide the molecular evidence for telltale vitamin deficiencies, even indicate "who ate who" in a prehistoric ecosystem. That’s the way it works for analysis of modern-day animal and human specimens as well.
"If you handed me a little piece of hair, I could tell you whether your cow ate corn or ate grass in Michigan," she said. The analysis could even determine whether a vegan was cheating on his or her diet, she added, half-jokingly.
Meanwhile, Schweitzer is trying to find out how much chemical information she can extract from the soft tissues within a T. rex fossil. "The preliminary data is kind of intriguing," she told reporters.
Ostrom said Schweitzer "should at some point be able to obtain a protein sequence or a DNA sequence," depending on how well the soft-tissue samples have stood up chemically.
"Are they proteins, or are they so altered that we can’t get their sequence," Ostrom asked rhetorically.
In any case, last year’s findings have led paleontologists to rethink the fossilization process. It was once thought that fossil bones were completely mineralized, destroying all traces of the organic chemicals within. "We know now that it has the real organic matter in it," Ostrom said.
Schweitzer said she and her colleagues were still trying to understand the conditions under which soft tissue can survive. It might have something to do with the increased density of the bones involved, or whether the bones were preserved in sandstone as opposed to mudstone.
"Whatever is going on, it seems to be relatively prevalent," Schweitzer said.
Other dinosaur experts shed additional light on the life of a tyrannosaur:
- The bones of maturing tyrannosaurs appear to follow a pattern much more similar to those of birds rather than crocodiles, strengthening the link between the extinct species and present-day birds. Paleontologist Jack Horner of the Museum of the Rockies in Bozeman, Mont., said the evidence can be seen by slicing T. rex bones into thin cross-sections, then analyzing the spaces that were once taken up by blood vessels. "The blood that went through the dinosaur bones is equal to or higher than what went through bird bones," Horner said. In contrast, modern-day crocodilians have much lower blood flow.
- T. rex appears to have had sensory systems that were "even more heightened than we thought," said Ohio University paleontologist Lawrence Witmer. That’s based on CT scans of fossilized dinosaur skulls that can indicate the size of areas devoted to particular tasks. Such an analysis indicates that T. rex had "an inner ear structure consistent with a dynamic lifestyle involving rapid tracking movements of the eyes and head," Witmer said. Based on brain size, the senses of smell, sight, hearing and balance were also relatively well-developed.
- T. rex was not particularly agile — even though it’s portrayed that way in "Jurassic Park" and other dinosaur movies. Based on the biomechanical evidence, Witmer and Horner agreed that T. rex couldn’t jump or run in the sense of having both feet off the ground at once. "We have an animal that looks like it should be agile, but isn’t. … I don’t think T. rex could dance," Horner said.
Although there are still plenty of mysteries to be settled about T. rex and its extinct kin, Witmer marveled at how much progress has been made already in figuring out how dinosaurs lived. A decade ago, "nobody would be even asking the kinds of questions that Jack and I are asking," he said. Now, he said, "we’re starting to answer them."
Tissue fragments from a Tyrannosaurus rex femur are shown at left, when it is flexible and resilient and when stretched (arrow) returns to its original shape. The middle photo shows the bone after it is air dried. The photo at right shows regions of bone that exhibit a fibrous character not normally seen in fossil bone.