Seismosaurus proteins: bone of contention.
W. Dale Spall and his colleages at Los Alamos (N.M.) National Laboratory chemically extracted the proteins from the vertebra of an enormous sauropod dinosaur -- with an estimated length of 160 feet -- excavated in central New Mexico. The record-breaking animal unoffcially dubbed seismosaurus, or "earth shaker," lived in the late Jurassic period, making these by far the oldest known proteins, says Spall, who described his team's work at a Geological Society of America meeting in Albuquerque.
Other researchers argue that the proteins may hail from much more recent times. "Perhaps [Spall and his co-workers] have proteins there, but there are proteins everywhere. They are easy to contaminate. You have them in your thumbprints and they exist in ground-water, wherever organisms can exist," says P. Edgar Hare, a geochemist with the Carnegie Institute of Washington (D.C.)
The Los Alamos team drilled a core out of the huge vertebra and used solvents to strip away the mineralized portion. High-pressure liquid chromatography revealed two or perhaps three proteins within the sample, they report.
The researchers did not extract enough material to identify the proteins they found, but they say their analysis of the amino acids in the molecules indicates the proteins are not collagen, the most abundant protein in bone.
Chemists have long wondered whether fossils might contain ancient biological molecules, but only recently have they developed sophisticated techniques that can analyze the very small samples extracted from bone. While researchers have identified free amino acids in animal fossils dating back several hundred million years, Spall says most investigators assume that proteins -- cannot remain intact for many millions of years.
At the outset, he says, "I didn't think we'd find anything." but the bones appeared exceptionally well preserved, perhaps explaining why the proteins survived. He and his colleagues have collected more seismosaurus bone samples, hoping to sequence and identify the proteins. They also plan to perform an amino acid analysis that can reveal whether the proteins are truly ancient.
Spall says their techniques for sampling and analysis avoid obvious contamination from human contact, but he adds that protein from groundwater may have seeped in while the fossil lay encased in sandstone for 150 million years. If so, he says, the isolated proteins would not belong to the dinosaur.
Stephen A. Macko, a geochemist at the University of Virginia in Charlottesville, raises another potential problem. He suggests that the material extracted by Spall might not be protein at all, but rather a nonbiological molecule that contains amino acids. "Further characterization of the material by other techniques should be in order before calling it a protein," says Macko, who recently helped isolate potential protein remnants from 66-milion-year-old dinosaurs.
The oldest proteins generally accepted by scientists date back only 1 or 2 million years, Hare says. But if investigators can isolate proteins belonging to much more ancient animals, they can use amino acid sequences to reinterpret relationships among species. For instance, scientists might compare bone proteins from dinosaurs, birds and reptiles to determine how closely these groups cluster on the tree of life. "Using a biochemical point of view to look at how organisms evolved would be a very powerfl approach for interpreting the fossil record," Macko says.