115-Million-Year-Old Brazilian Dinosaur Bone Preserves Fossilized Blood Cells and Hemoglobin

Researchers describe a 115-million-year-old dinosaur bone from the Romualdo Formation in northeast Brazil that preserves tiny red-blood-cell-like structures and traces of blood molecules inside the bone.

The discovery, reported in PNAS and written by The Conversation, provides direct molecular clues about ancient life and demonstrates that soft tissues and biomolecules can endure for millions of years under the right conditions.

• Structures lie exclusively in vascular canals inside the bone, mirroring the location of red blood cells in living vertebrates.
• Chemical fingerprints dominated by heme molecules indicate preserved blood within the fossil bone, distinct from surrounding sediment.
• The specimen is Aratasaurus museunacionali, whose name honours Brazil's National Museum and its fire past.
• Rapid burial in a low-oxygen environment and stabilizing minerals may slow decay and help preserve molecules over tens of millions of years.

Background

The Romualdo Formation in northeast Brazil is famed for exceptional fossil preservation, including fish, turtles, crocodile relatives and pterosaurs. A team of researchers from Brazil, Japan and the United States studied a remarkably well-preserved partial hind limb of a small dinosaur named Aratasaurus museunacionali, which is housed in a palaeontology museum in northeast Brazil. The specimen survives in a context where the site’s geochemistry has preserved fine anatomical detail rarely seen elsewhere. The species name museunacionali honors the National Museum in Brazil, whose collection history is marked by the 2018 fire that destroyed much of the museum's holdings, though the fossil studied here was unaffected by the blaze. The genus name combines Tupi and Greek roots to reflect a dinosaur “born from the National Museum fire.”

The Discovery and Significance

Researchers sought to determine whether the visible structures inside the bone were genuine biological remnants or later artefacts of fossilisation. They found that the structures are located within vascular canals inside the bone, the same niche where red blood cells are found in living vertebrates. In contrast, the surrounding sediment did not contain these structures, making external contamination unlikely. After evaluating multiple alternative explanations, the team concluded that they most likely represent fossilised red blood cell remnants, a claim that, if confirmed, would extend the timeframe over which soft tissues and biomolecules can be preserved in fossils.

Chemical Fingerprints of Ancient Blood

To fortify their interpretation, the researchers identified two chemical fingerprints with the structure of heme, a key component of haemoglobin that ferries oxygen in blood. A stark contrast emerged between the sediment’s chemistry and the fossil interior: the sediment contained plant- and bacteria-derived compounds, while the fossil bone showed a signature dominated by heme-related molecules. Additional analyses detected elements including iron, carbon and nitrogen, as well as amino acids consistent with collagen, which is a major connective tissue component. This multi-faceted molecular geochemical approach strengthens the case that the bones preserve blood-derived materials.

Preservation Through Deep Time

The team proposes that the dinosaur was rapidly buried in a low-oxygen setting, slowing decay and enabling blood-derived materials to persist. The researchers suggest that microscopic red blood cells may have transformed into minerals during fossilisation, a process that can trap and stabilise delicate organic molecules. A mineral such as hausmannite could act as an antioxidant and slow down the breakdown of sensitive biomolecules, further extending their persistence. Taken together, these conditions could preserve information at the molecular level for more than 100 million years, reshaping expectations about fossil preservation and the kinds of data accessible in museum collections.

Implications for Paleontology and Museums

This discovery highlights that soft tissues and biomolecules—long considered unlikely to survive for tens of millions of years—can persist under certain circumstances. It opens the possibility that other fossils stored in museums around the world may harbor molecular, chemical and environmental information worth revisiting with modern analytical methods. The Conversation notes that techniques such as microscopy, mineralogy, spectroscopy and molecular geochemistry can be deployed to re-examine established specimens to extract new insights about ancient life and its biology.

Collaborators and Access

The fossil was collected and curated through collaborations involving Renan Bantim and Antônia Saraiva of the Regional University of Cariri, Juliana Sayão and Alexander Kellner from Brazil’s National Museum and the Federal University of Rio de Janeiro. Additional partners include Yuta Isaji, Calum Fox, Nana Ogawa and Noa Ohkouchi from the Japan Agency for Marine-Earth Science and Technology and Jasmina Wiemann from Johns Hopkins University. The study underscores the importance of international partnerships in unlocking the scientific value of existing fossil collections and museum assets.