The tiny fossil is unassuming, as dinosaur remains go. It is not as big as an Apatosaurus femur or as impressive as a Tyrannosaurus jaw. The object is a just a scant shard of cartilage from the skull of a baby hadrosaur called Hypacrosaurus that perished more than 70 million years ago. But it may contain something never before seen from the depths of the Mesozoic era: degraded remnants of dinosaur DNA.
Genetic material is not supposed to last over such time periods—not by a long shot. DNA begins to decay at death. Findings from a 2012 study on moa bones show an organism’s genetic material deteriorates at such a rate that it halves itself every 521 years. This speed would mean paleontologists can only hope to recover recognizable DNA sequences from creatures that lived and died within the past 6.8 million years—far short of even the last nonavian dinosaurs.
But then there is the Hypacrosaurus cartilage. In a study published earlier this year, Chinese Academy of Sciences paleontologist Alida Bailleul and her colleagues proposed that in that fossil, they had found not only evidence of original proteins and cartilage-creating cells but a chemical signature consistent with DNA.
Recovering genetic material of such antiquity would be a major development. Working on more recently extinct creatures—such as mammoths and giant ground sloths—paleontologists have been able to revise family trees, explore the interrelatedness of species and even gain some insights into biological features such as variations in coloration. DNA from nonavian dinosaurs would add a wealth of new information about the biology of the “terrible lizards.” Such a find would also establish the possibility that genetic material can remain detectable not just for one million years, but for tens of millions. The fossil record would not be bones and footprints alone: it would contain scraps of the genetic record that ties together all life on Earth.
Yet first, paleontologists need to confirm that these possible genetic traces are the real thing. Such potential tatters of ancient DNA are not exactly Jurassic Park–quality. At best, their biological makers seem to be degraded remnants of genes that cannot be read—broken-down components rather than intact parts of a sequence. Still, these potential tatters of ancient DNA would be far older (by millions of years) than the next closest trace of degraded genetic material in the fossil record.
If upheld, Bailleul and her colleagues’ findings would indicate that biochemical traces of organisms can persist for tens of millions of years longer than previously thought. And that would mean there may be an entire world of biological information experts are only just getting to know. “I think exceptional preservation is really more common than what we think, because, as researchers, we have not looked at enough fossils yet,” Bailleul says. “We must keep looking.”
The question is whether these proteins and other traces are really what they seem. Hot on the heels of Bailleul’s paper—and inspired by the controversy over what the biomolecules inside dinosaur bones represent—a separate team, led by Princeton University geoscientist Renxing Liang, recently reported on unexpected microbes found inside one from Centrosaurus, a horned dinosaur of similar age to Hypacrosaurus. The researchers said that they unearthed DNA inside the bone, but it was from lineages of bacteria and other microorganisms that had not been seen before. The bone had its own unique microbiome, which could cause confusion as to whether proteins and possible genetic material belonged to the dinosaur itself or to bacteria that had come to reside within it during the fossilization process.
The discovery that such fossils can harbor bacterial communities different from those in the surrounding stone complicates the search for dinosaur DNA, proteins and other biomolecules. The modern may be overlaid on the past, creating a false image. “Even if any trace organics could be preserved,” Liang says, “the identification processes would be as challenging as finding a needle in the haystack and thus will likely lead to potential false claims.”
“Right now, molecular paleontology is controversial,” Bailleul says. The first sticking point is that when researchers look for traces of ancient biological molecules, they use technologies invented to find intact traces that have been degraded or altered by vast amounts of time. On top of that issue, there remains much experts do not know about how a dinosaur bone changes from organic tissue in a recently alive animal to a fossil hardened by minerals. “We have not figured out all of the complex mechanisms of molecular fossilization using chemistry. And we don’t know enough about the roles that microbes play,” Bailleul says. For example, it is unclear how modern microbes outside of fossils might interact with those that have been living within the bones.
These unknowns, as well as protocols that are still in development, fuel the ongoing debate over what the biological tidbits inside dinosaur bones represent. The research on the Hypacrosaurus cartilage looked at its microscopic details and used chemical stains that bind to DNA. In contrast, the study on the Centrosaurus bone used DNA sequencing to understand the nature of the genetic traces inside it—but did not look at its microstructure.
Bailleul acknowledges that considering previously unknown forms of microorganisms when studying dinosaur bone microbiology is important. But she proposes that it is unlikely bacteria would find their way into a cartilage cell and mimic its nucleus in such a way that researchers would mistake the microorganisms for the genuine article. Yet “you can never be too skeptical of your own results,” says paleogeneticist and author Ross Barnett, who was not involved in the two studies described above.
One of the largest difficulties in the ongoing debate, Barnett says, is a lack of replication. And paleogenetics has been through this problem before: Around the time the film Jurassic Park debuted in 1993, research papers heralded the discovery of Mesozoic DNA. Those claims were later overturned when other research teams could not replicate the same results. Even though the science of paleogenetics has changed since that time, the need for multiple labs to confirm the same result remains important. “If a different lab could be independently sent fossils from the same site, work up their own antibodies, do their own staining and get the same results, it would make things more believable,” Barnett says. Such collaboration has yet to take place for some of the assertions of exceptional dinosaurian preservation.
Nevertheless, molecular paleobiology is developing standards of evidence and protocols as it continues to search for clues held inside ancient bones. “I hope that many paleontologists or biologists, or both, are also trying to do this,” Bailleul says. “We can figure out the answers faster if we are all working on this together.”
Even if proposed dinosaur organics turn out to be false, the effort could still yield unexpected benefits. Bacterial communities are thought to be involved in the preservation of bones and in their replacement with minerals, thus helping dinosaur remains become fossils. “Future studies about ancient DNA from past microbial communities that used to live inside the dinosaur bones could shed more light on the roles of microorganisms in the fossilization and preservation of bones through geological time,” Liang says.
“These are very difficult questions,” Bailleul says. “But if we keep trying, there is hope that we will figure out most answers.” As the situation stands now, nothing is written in stone.