For all but the last decade of paleontology, scientists have based their understanding of dinosaurs on fossilized bone. Unlike soft tissue (muscle, skin, blood vessels), which decays, bone lasts long enough that minerals from the surrounding mud and water can slowly replace the minerals inside cells, turning the hard tissue to rock.
Although fossils illuminate a great deal about the appearance and behavior of extinct animals, they can't be examined with the tools of modern molecular biology. At least, they couldn't until 2005, when North Carolina State University researcher Mary Schweitzer discovered preserved blood and collagen in the bones of a 68-million-year-old Tyrannosaurus rex. Since then, there have been a handful of other soft tissue finds in fossils from the late Cretaceous, the period that ended with a mass extinction 65 million years ago after an asteroid hit the Earth.
Having soft tissue “lets you ask the really cool questions,” Schweitzer told The Washington Post recently. “Can we directly compare these molecules to now and see how they've changed? That gets at rate and time of evolution. … Can we pull out sequences of microbes, is there a way we can study coevolution of disease processes?”
More and more paleontologists are now probing for soft tissue in their fossil finds, including Robert Reisz, a researcher at the University of Toronto Mississauga. In 2013, he wrote a study on the discovery of possible organic remains inside an embryonic Lufengosaurus. But the material couldn't be identified more specifically, so he and his colleagues set off in search of some better preserved tissue.
In this latest study, they say they've found it. Using a synchrotron to create high-power beams of infrared light, Reisz's collaborators at the National Synchrotron Radiation Research Center in Taiwan probed the vascular canals of their Lufengosaurus rib, which once contained blood vessels and protein. By analyzing the wavelengths of light that bounced back, they could figure out the molecular composition of the material inside the rib. It contained several key proteins characteristically found in collagen, the oldest evidence of proteins ever detected.
The scientists also found crystals of hematite, the mineral form of iron oxide. Since the rocks around the fossil are iron-poor, Reisz said that the hematite probably comes from the iron-rich blood cells of the dead dinosaur. “We don’t have the blood cells,” he said. “We don’t have the organic remnants, but we do have the iron that was in the blood.”
Hematite can act as a preservative, Reisz said, perhaps explaining how the collagen persisted so long after the dinosaur's death. “The indication that there is collagen here is really exciting, because it tells us that you are not restricted to the late Cretaceous in being able to identify soft tissue,” he said.
Proteins like collagen are the body's workhorses, carrying out the jobs dictated by an organism's genetic blueprint. Although DNA is very fragile, and unlikely to persist for millions of years, proteins can offer almost as good a window onto the way ancient creatures lived, according to Reisz. “Anything organic can be very useful in comparing these extinct animals to living things,” he said.
Reisz's study is also promising because it used techniques to identify the remains while preserving them. Most searches for dinosaur soft tissue, including Schweitzer's, have required that scientists grind up the fossil or use acid to dissolve the surrounding bone. ("People tend to lock their collections doors when they see me,” Schweitzer joked.) By studying the material at its synchrotron, Reisz and his team were able to avoid losing their fossil in the process.
But Schweitzer cautioned that the form of spectroscopy used by Reisz and his colleagues is so sensitive that it could pick up even small amounts of contamination. She said that she would like to see the team provide more lines of evidence for their claim, especially since soft tissue discoveries are controversial in the paleontology world.
Still, she added, synchrotrons are sure to become another powerful tool for biologists studying living species and dead ones.
“I think as we get more information from living organisms we will get more information from extinct ones,” she said. “Does that have implications for our future? Maybe it does. We can’t possibly predict where we’re going if we don’t know where we came from.”
Correction: A previous version of this article misidentified the journal in which Reisz's study was published. It is Nature Communications.