Scientists report chemical traces of red blood cells in a 115-million-year-old dinosaur bone

A team of paleontologists and geochemists says it has found some of the strongest chemical evidence yet that fragments of blood-related biomolecules can survive inside dinosaur bone for well over 100 million years. The claim, published Nov. 2 in the Proceedings of the National Academy of Sciences, centers on a single fossilized leg bone recovered from a quarry in northeastern Brazil.

The bone belonged to Aratasaurus museunacionali, a small, feathered theropod that lived roughly 115 million years ago during the Early Cretaceous period, in what is now the Araripe Basin of Ceará state. Researchers led by Kliti Grice, a geochemist at Curtin University in Perth, examined the animal's hind-limb bones and reported numerous tiny, ellipsoidal structures — on the order of 20 to 23 microns across, roughly the size of a modern red blood cell — lodged inside the bone's vascular canals, the narrow channels that once carried blood vessels through living tissue.

What the analysis found

Using scanning electron microscopy, Raman spectroscopy, transmission electron microscopy and high-performance liquid chromatography paired with mass spectrometry, the team detected heme B, the iron-containing molecule at the functional core of hemoglobin, along with a chemically altered derivative of it. According to a Reuters report on the findings, the researchers argue the structures are mineralized remnants of red blood cells, preserved in part because they became encased in hausmannite, a manganese oxide mineral the team describes as having acted like "a natural time capsule."

Grice said the detection of heme-derived molecules inside cell-shaped structures of that age surprised even the research team. "Our findings challenge longstanding assumptions that certain biomolecules such as hemoglobin cannot survive deep time," she said, according to the university release, adding that the result "extends the known fossil record of blood" by a wide margin. Soft-tissue traces had previously been reported in dinosaur bone, including decades-old work on structures resembling blood vessels and cells in Tyrannosaurus rex specimens, but direct chemical confirmation of a hemoglobin-related molecule at this age is new, the team says.

The specimen's path to publication took an unusual route. According to Brazilian National Museum paleontologist Alexander Kellner, a co-author on the study, the fossil was recovered years ago from a gypsum mine in Ceará and was later sent to the museum's preparation lab — housed in a wing that survived the 2018 fire that destroyed much of the institution's main collection — before a small sample was set aside for the geochemical analysis reported in the new paper, as described in a summary by Sci.News and in wire-service reporting on the study.

Why the finding matters, and its limits

If the interpretation holds up, the result would matter beyond a single fossil. Molecular traces inside bone, however fragmentary, can in principle offer researchers a more direct window into the physiology of extinct animals — metabolism, activity levels, even aspects of how blood itself evolved — than skeletal anatomy alone allows. Grice described the work as opening "exciting new avenues for molecular-level paleontology."

But the authors themselves are careful to frame what was, and was not, found. The paper does not claim to have recovered intact blood, functioning hemoglobin protein or any dinosaur DNA. Grice has said plainly that "morphology by itself isn't enough to establish its biological origin," acknowledging that the shape of a structure cannot, on its own, prove it began as a living cell rather than forming through non-biological mineral processes after burial. The team also could not entirely rule out that heme-producing microbes, rather than the dinosaur's own blood, contributed to the chemical signal.

"Our findings challenge longstanding assumptions that certain biomolecules such as hemoglobin cannot survive deep time," said Kliti Grice, the study's lead author at Curtin University.

That caution is shared by scientists outside the study. The question of whether soft-tissue-like structures in dinosaur bone represent genuine biological remnants or later mineral artifacts has been debated for roughly two decades, since North Carolina State University paleontologist Mary Schweitzer first reported probable blood vessels and cells in T. rex bone in the mid-2000s. Schweitzer, who was not involved in the new study, has raised doubts about the Brazilian specimen as well, noting in coverage of the paper that the structures described are smaller than typical non-mammalian red blood cells and arguing that size and shape alone fall short of establishing their biological origin.

What happens next

The researchers say further work will focus on testing whether similar heme signatures turn up in other fossils from different environments and time periods, which could help settle whether hausmannite mineralization — or some similar process — is a genuinely reliable preservation pathway rather than a one-off. The study drew on a multi-institution collaboration, including geochemists and paleontologists at Curtin, Brazil's National Museum and the Regional University of Cariri, Japan's Agency for Marine-Earth Science and Technology, and Johns Hopkins University, reflecting the range of imaging and chemical techniques needed to make the case.

For now, the finding stands as a contested but closely scrutinized data point in a long-running scientific argument over just how much of a 115-million-year-old animal can, in any real sense, still be there to study.