Scientists studying a 115 million-year-old dinosaur bone say they have found the strongest evidence yet of red blood cells in a fossil.
Paleontologists dug up the leg bone in 2008 at the geological site Mina Pedra Branca in northeastern Brazil within the Romualdo Formation, a rocky area known for its exceptionally preserved fossils, as reported by CNN.
The regional area belongs to the Araripe Basin, famous among paleontologists for the quality of its fossils. Scientists believe stagnant waters limited oxygen and slowed the decomposition of remains buried in this region.
The fossil is a partial hind limb of Aratasaurus museunacionali, a theropod dinosaur that lived during the Early Cretaceous. According to Yahoo, the fossil is the lucky survivor of a 2018 fire that destroyed the National Museum at the Federal University of Rio de Janeiro.
A local resident donated it to the paleontology museum of the Regional University of Cariri, which is named after Plácido Cidade Nuvens. The specimen arrived as a dark stone slab measuring about 4 by 2.6 feet, holding part of the right hind leg from thigh to foot.
The animal was a small feathered theropod, likely a young individual about 10 feet long and weighing 75 pounds, probably about four years old and still growing.
The researchers prepared thin cross-sectional slices of bone and imaged details of the limb bone’s internal structure.
To identify molecules by how they scatter laser light, the team used specialized analysis and ruled out contamination from other porphyrins, such as chlorophyll, by separating and identifying the molecular contents of a bone extract.
Extracts of the bone contained heme-related compounds, while the surrounding rock had a different chemical signature. An international team led by Curtin University reported the findings.
The findings published in the Proceedings of the National Academy of Sciences strengthen the argument that biological structures and molecules can survive in prehistoric fossils, said lead author Kliti Grice, an organic geochemist and John Curtin Distinguished Professor at Curtin University in Perth, Australia, as noted by CNN. The team reported the discovery on November 2, 2026.
Lead author Kliti Grice, an organic geochemist and John Curtin Distinguished Professor at Curtin University, said “The exciting implication is not just what we have found in this dinosaur. It is that we now have approaches that can be applied to other fossils to ask how much original biological information may still be hidden within them”
The authors propose that minerals acted as a natural antioxidant, neutralizing the aggressive molecules that usually break organic matter down. An oxygen-poor, sulfur-rich setting slowed the damage further, while a complex manganese oxide called hausmannite helped maintain cellular structures and stabilize amino acids from collagen.
Grice said “Bones provide extraordinary information about anatomy, growth, locomotion and evolution. But cellular and molecular preservation potentially gives us access to a different layer of biological information: the chemistry of the living animal and its tissues”
However, not all experts are convinced that the microscopic structures are truly red blood cells. Mary Schweitzer told ABC News that some of the fossil structures appeared smaller than expected and lacked the characteristic central bulge associated with nucleated cells.
Will future applications of this in-place approach resolve whether these structures are definitively red blood cells?
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