Hints of fossil DNA discovered in dinosaur skull

March 7, 2020

For billions of years, DNA has served as life’s information molecule, containing instructions for how and when to build the proteins of living organisms. But how long can that biological information survive? In a provocative new study, an international team of researchers reveals dinosaur fossils that are so well preserved, some contain the outlines of cells—and structures that might have formed from the dinosaurs’ original DNA.

The study, published last week in National Science Review, takes a close look at two juvenile skull bones from the hadrosaur Hypacrosaurus stebingeri, a plant-eating dinosaur that lived in what’s now Montana about 75 million years ago.

Inside the tiny fossils, researchers can see what appear to be cells, some frozen in the process of dividing. Others contain darkened balls that look just like nuclei, the cellular structures that store DNA. And one cell even seems to contain dark, tangled coils that resemble chromosomes, the condensed strands of proteins and DNA that form during cell division.

02_dna_fig1-new-mor548-paleohisto-01.adapt.676.1.jpg To test the fossilized material, the researchers applied stains that bind to DNA in living cells to the bits of dinosaur skull. These stains stuck to particular spots within the fossil cells, making them glow in fluorescent red and blue. As far as the researchers can tell, whatever the stains are binding to derived from the dinosaur’s original molecules, not an outside contaminant such as bacteria.

If intact DNA is present in these dinosaur fossils, scientists may need to reappraise the molecule’s ruggedness. Past studies have found that genetic material disintegrates in bones after a few million years. The oldest complete genome ever sequenced comes from a 700,000-year-old horse bone found in Siberia, frozen in the permafrost since the animal’s death—and the Hypacrosaurus bones are about a hundred times older.
Bones are highly porous in life, which makes them imperfect time capsules in death. The preserved dinosaur cells were probably embedded in cartilage, Schweitzer says, which lacks pores. The structure of cartilage may have protected the cells inside—and their chemical constituents—more effectively.

“Fossilized, calcified cartilage may be an ideal place to search for exceptionally preserved biomolecules in other fossils, as this tissue may be less prone to contamination and internal decay than bone,” Evans says. “In calcified cartilage, the cells become trapped and isolated in their matrix and are more likely to be preserved in a sealed micro-environment.”