Possible Red Blood Cells Found in a 115 Million-Year-Old Dinosaur Bone

A team of researchers says it has found what appear to be fossilized red blood cells inside a dinosaur bone that is 115 million years old, along with chemical traces of heme, the molecule that lets blood carry oxygen. The study was published Nov. 2 in the Proceedings of the National Academy of Sciences, according to The Guardian and Live Science.

Not every expert agrees. A leading researcher of dinosaur soft tissue told both outlets she is not convinced the structures are red blood cells, though she found other parts of the work persuasive.

What the researchers found

The bones come from Aratasaurus museunacionali, a small, meat-eating theropod about 10 feet (3 meters) long that lived in what is now north-eastern Brazil, the Guardian and Live Science reported. The remains were found in a mine in 2008 and are held in the National Museum of Brazil.

Kliti Grice, a professor at Curtin University in Western Australia who led the work, spotted the structures while studying hind leg bones. Electron microscope images showed small, round shapes in the fine channels where blood vessels once ran. Live Science said the team found numerous such structures inside these vascular canals and that their shape, size and location were consistent with red blood cells.

Chemical tests then found heme and its breakdown products, according to the Guardian. The bone also contained amino acids that are building blocks of collagen, a structural protein in bone and other tissues.

Grice told Live Science the team was not originally looking for blood. Her question was how much of an ancient organism's biology can survive fossilization. She said the researchers tested the chemistry in the bone itself, which let them tie chemical signals to the microscopic structures in place, rather than extracting molecules and guessing where they came from.

How the cells could have survived

Biological tissue usually breaks down quickly, which is why such claims are controversial. Grice suggested a manganese mineral called hausmannite formed in and around the cells and may have stabilized them before fossilization, the Guardian reported. She said the same process might have helped preserve the amino acids.

Live Science added that the team thinks the animal was quickly buried in sediment in a low-oxygen setting with microbial mats, thin films of microorganisms. Those conditions may have slowed normal decay.

Why a leading expert is skeptical

Mary Schweitzer, a molecular paleontologist at North Carolina State University who was not involved in the study, praised the team for bringing rigor to the study of fossils from deep time. She agreed that molecules produced by the body can persist over geological time in some form.

But she told Live Science she does not think the images show red blood cells. Birds and reptiles, unlike mammals, keep their nuclei in red blood cells, which typically gives the cells a nuclear bulge and a dome-like look on both sides. Schweitzer said the structures in the study are concave, with no such bulge, and are smaller than most non-mammalian red blood cells. In her view, the shape does not match, and the Guardian reported that she thinks they might be something else.

She also suggested that resonance Raman spectroscopy, a technique that characterizes chemical compounds, would have given more conclusive evidence. Her team used it in 2025 to detect heme in tissues from Brachylophosaurus canadensis and T. rex, Live Science reported. Schweitzer was more persuaded by the heme and collagen amino acids found in the bone.

What this means

If the claim holds up, scientists could one day study dinosaur blood, metabolism and even activity levels, the Guardian reported. Grice said the finding suggests that museum collections around the world may already hold molecular information waiting for new questions.

She urged caution, though. She said the work does not imply that large molecules such as proteins or DNA survive in ancient fossils. In her words, “This is a world first” for red blood cells with distinct heme chemistry found in place in a fossil, but she also said extraordinary claims need extraordinary analytical evidence. Live Science described the result as the oldest chemical evidence of blood-related material in a dinosaur fossil, a claim that remains disputed.

Around Prague, based on reporting by The Guardian, Live Science