Cells from a 125 million-year-old dinosaur have been preserved so well that organic molecules survived in the nucleus of at least one. This is only the second time this has been observed in a Cretaceous fossil, and by far the oldest. The finders have yet to extract DNA from these cells, let alone sequence it, and are not claiming it is possible. However, they think it cannot be ruled out and, if achieved, it would represent an opportunity to learn about dinosaur genetics to an extent previously barely contemplated.
In the early Cretaceous, Liaoning Province, China, contained some shallow lakes whose shores were attractive feeding grounds for dinosaurs. Unfortunately for those animals (but fortunately for paleontologists) the area was then also highly volcanic.
"Geological data has accumulated over the years and shown that fossil preservation in the Jehol Biota was exceptional due to fine volcanic ashes that entombed the carcasses and preserved them down to the cellular level," said Dr Li Zhiheng of China's Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) in a statement.
Zhiheng and co-authors extracted cartilage from the Caudipteryx's right femur and decalcified it. Analysis revealed the cells had been impregnated with silicon, preserving them so well the team could tell the health of individual cells when they were fossilized, some of which were already in bad shape. "It is possible that these cells were already dying even before the animal died," said IVPP's Dr Alida Bailleul.
The authors stained the cells with hematoxylin, which binds to cell nuclei. In one cell this revealed not only a nucleus with biomolecules intact, but threads of chromatin, which is formed from tightly packed DNA bound with proteins. This doesn't mean the DNA has survived to an extent that would allow the team to sequence it, but Bailleul thinks there might be a chance.
“Let's be honest,” she said. “We are obviously interested in fossilized cell nuclei because this is where most of the DNA should be if DNA was preserved.”
The oldest sequenced DNA dates back 1.2 million years, and anything of similar age is usually trapped in ice. Finding DNA from 125 million years ago would be an astonishing jump. Nevertheless, the authors claim their work proves it is possible for cells that old to survive while not being truly “stonified”.
Even if the DNA can be sequenced, we're a long way from a Jurrasic Park resurrection scenario. Moreover, Caudipteryx isn't what comes to mind when one thinks of dinosaurs, being the size of a modern peacock and likewise equipped with impressive tail feathers. Nevertheless, its DNA would, if sequenced, provide extraordinary insights into theropod dinosaur evolution.
Bailleul led a team that last year reported finding possible preserved DNA from a 75 million-year-old hadrosaur found in Montana. In that case the cells were also preserved within cartilage, which being less porous than bone, protects against water and microbial infiltration. The paper notes cartilage is a greatly understudied resource compared to bones and teeth in both paleontology and forensics. Perhaps that is about to change.