Study claims 115-million-year-old dinosaur blood traces survived

They propose that hausmannite acted as a time capsule, stabilizing the cell-like forms and protecting biological molecules, including collagen amino acids, as the bone fossilized. The close positioning of mineral, structures and heme signatures suggests, in the team’s view, a previously unrecognized preservation pathway.

That distinction matters. Fossilization can introduce mineral-rich fluids that create shapes resembling tissues. In a 1997 study, two paleontologists examined tiny spheres in the limb of a fossil, possibly a pterosaur, once proposed as blood cells. They determined that the spheres were pyrite, an iron mineral deposited after death.

The 1997 researchers suggested several tests before calling microscopic structures blood cells. Examples included comparing their shape with living relatives and finding specific biomarkers, including heme compounds. Grice and her colleagues say their study passes those tests.

Grice said hausmannite was crucial to preservation, “rather than simply a mineral that replaced biological material after it had disappeared.” Its spatial relationship with the cell-like structures and chemical evidence, she said, supports the idea that mineralization stabilized, entombed and protected the original material.

Why does an outside expert dispute the claim?

Mary Schweitzer, a paleontologist at North Carolina State University in Raleigh who did not take part in the study, says the criteria remain unmet. The heme signals, for example, came from analysis of the whole bone and did not appear confined to the round structures where blood-cell remnants should be concentrated.

She also says the proposed cells differ in size and shape from red blood cells in living birds and reptiles. That comparison remains uncertain because no one knows what a dinosaur’s red blood cells should have looked like.

Schweitzer has challenged claims about ephemeral tissues before. In 2005, she and colleagues reported the first recovery of flexible, soft-tissue blood vessels from a 68-million-year-old fossilized leg bone of a Tyrannosaurus rex. The landmark work prompted debate over whether such tissues could survive deep time and how to detect them reliably.

“I am not convinced” that the team has definitively identified heme compounds, Schweitzer said. “I do applaud them for bringing a plethora of methods to the study. Extraordinary claims require extraordinary evidence, and that does require state-of-the-art technology.”

Grice acknowledges the uncertainty. She said no one knows what a dinosaur red blood cell looked like, how fossilization might distort its shape, or whether heme-related molecules could migrate out of a cell’s boundaries over millions of years. Her team’s answer rests on convergence, not any single test: anatomy, morphology, mineralogy, elemental analysis and molecular chemistry.

Whether hausmannite preserved blood traces in other fossils remains unknown. Grice said the team does not know yet, while suggesting this form of preservation may be less rare than current evidence indicates.

What does this change for dinosaur physiology?

The discovery could give paleontology a molecular window into long-extinct animals, including their metabolism and activity levels, Grice said. That is the practical promise. The present evidence, however, comes from one fossil specimen, the identity of the structures remains disputed, and the proposed preservation pathway has not been demonstrated elsewhere.

For now, the study expands what scientists can look for and test; it does not establish that dinosaur blood routinely survives fossilization. The verdict remains open.