Fossilized Heme and Possible Red Blood Cells Found in 115-Million-Year-Old Dinosaur Bone
Microscopic and chemical analysis of an Aratasaurus bone from Brazil has revealed in situ heme and cell-like structures, prompting debate over whether intact red blood cells can survive 115 million years.
For decades, the standard assumption across vertebrate paleontology was that delicate organic molecules and cellular structures could not survive deep geological time, leaving behind only mineralized bone and stone impressions. A paper published in PNAS has challenged that view, reporting the identification of structures resembling red blood cells and chemical evidence of heme in a 115 million-year-old theropod dinosaur bone from Brazil. Using a combination of microscopic imaging and chemical analyses, researchers uncovered evidence that biological traces may persist inside fossil bone far longer than previously thought possible.
The fossilized bone belongs to Aratasaurus, a theropod dinosaur discovered in Brazil. Within the vascular canals running through the fossil, where blood would have flowed during the animal’s life, the research team documented oval-shaped microstructures that closely mimic blood cells. Chemical tests subsequently identified heme inside the tissue, marking the first time the compound has been detected in situ in a dinosaur fossil.
Heme is the iron-bearing porphyrin that forms the oxygen-binding core of hemoglobin, making it central to blood transport in vertebrates. Finding its chemical signature intact within the vascular canals provides direct biochemical evidence of circulatory remnants that have survived 115 million years. Paired with additional chemical signatures of collagen, the discovery suggests that specific preservation microenvironments can shield soft-tissue components from total decomposition across vast spans of geological time.
The visual interpretation of the oval shapes, however, has drawn debate among paleontologists. While the authors interpret the find as fossilized red blood cells accompanied by distinct heme chemistry, outside researchers have raised doubts about whether the physical microstructures represent intact cells. Specifically, independent experts pointed out that the structures are concave rather than having the expected nuclear bulge characteristic of red blood cells. Non-mammalian vertebrates retain nuclei in their mature red blood cells, which generally creates a visible central swelling rather than a depressed, concave surface.
That structural difference leaves room for alternative explanations, such as mineral precipitates or degraded cellular debris that took on an oval morphology during fossilization. Yet even skeptical researchers emphasize that the chemical findings are far more difficult to dismiss than the cell-like shapes. The detection of heme alongside collagen signatures provides strong molecular support for the survival of genuine dinosaur soft-tissue compounds, regardless of whether the physical structures represent pristine, uncollapsed cells.
Whether the microscopic shapes turn out to be authentic fossilized cells or secondary structures preserving biological residue, the discovery represents a notable milestone in ancient biomolecule research. Paleontologists studying prehistoric life are no longer limited solely to gross skeletal anatomy. As spectroscopic and chemical analyses become standard practice on Mesozoic remains, the discovery demonstrates that ancient bone can retain detectable fragments of blood chemistry across more than a hundred million years.