Fossilised red blood cells and heme found in 115-million-year-old dinosaur bone

What the researchers found

Researchers led by Prof Kliti Grice of Curtin University in Western Australia report structures resembling fossilised red blood cells in the hind leg bones of an Aratasaurus, a small meat-eating dinosaur that lived about 115 million years ago in what is now north-eastern Brazil. The study appeared in the Proceedings of the National Academy of Sciences (PNAS) on Monday, 2 November 2026. Electron microscope images revealed round structures inside narrow channels that once held blood vessels. Chemical tests also picked up heme, the compound that lets haemoglobin carry oxygen, along with traces of its breakdown products and amino acids that build collagen, a key protein in connective tissue. Grice described the result as a "mineral and molecular echo" of the animal's original biology and said a confirmed finding would be without precedent.

“Fossilised red blood cells with distinct chemistry related to heme have never been found in situ in any fossil, let alone a dinosaur. This is a world first.”

How the analysis was done

The fossil remains were discovered in a mine in 2008 and have since been held by the National Museum of Brazil, where researchers continue to study them. Grice spotted the structures while analysing the hind leg bones, and the team combined microscopy, spectroscopy and molecular analysis to test whether they were really blood cell remains. The molecular signals inside the bone differed from those in the microbial layer surrounding the fossil, which the authors read as evidence that the markers came from the bone itself rather than from outside contamination. Co-authors come from the Japan Agency for Marine-Earth Science and Technology, the National Museum of Brazil, the Regional University of Cariri and Johns Hopkins University.

Preservation and open questions

The team points to hausmannite, a manganese compound that formed in and around the blood cells, as a possible stabiliser before fossilisation. Microbial activity and an oxygen-poor environment are also cited as factors that may have kept the material intact. Grice said the same process might have helped preserve the amino acids. The question of preservation is central, because biological tissues and molecules can break down quickly and leave little trace in ancient fossils.

Scepticism and what comes next

Such claims are controversial because biological tissues and molecules usually decay fast, so the significance of the result depends on whether the interpretation of the chemistry holds. Earlier work is also disputed. In 2005, a team led by palaeontologist Mary Schweitzer placed bones of a Tyrannosaurus rex in a solution that gradually dissolved the mineral, leaving flexible vessels with small round structures inside. Whether those were blood vessels and blood cells of the 68-million-year-old predator remains disputed, and a matching shape proves little without matching chemistry. If the interpretation holds, the researchers say the work could open new lines of inquiry into dinosaur blood, metabolism and activity levels.