Scientists Identify Potential Red Blood Cells in 115-Million-Year-Old Fossil

An international team of researchers has reported the discovery of microscopic structures resembling red blood cells within the fossilized remains of an Aratasaurus museunacionali, a theropod dinosaur that lived approximately 115 million years ago. The findings, published in the journal Proceedings of the National Academy of Sciences, suggest that biological molecules may persist in the fossil record far longer than previously believed possible by many in the scientific community.

The fossilized leg bone was originally unearthed in 2008 at the Mina Pedra Branca site within the Romualdo Formation in northeastern Brazil. This region is noted for its exceptional preservation conditions, which scientists believe were facilitated by stagnant, low-oxygen waters that slowed the decomposition of organic matter. The specimen, which survived the 2018 fire at the National Museum of Brazil, provided the material for this detailed analysis.

Using advanced microscopic imaging and chemical analysis, the researchers identified oval-shaped microstructures inside the bone's vascular canals. Beyond their appearance, the team detected chemical evidence of heme, a molecule integral to hemoglobin, the protein responsible for oxygen transport in red blood cells. Lead author Kliti Grice, a professor at Curtin University, described the find as an extraordinary mineral and molecular echo of the animal's original biology.

The study suggests that the preservation of these structures was potentially aided by the presence of hausmannite, a manganese oxide mineral. While the researchers believe this mineral formed during the fossilization process, they argue it acted as a natural capsule that helped stabilize the cellular structures and associated biomolecules over millions of years.

Despite the significance of the findings, the research has prompted debate among experts. Mary Schweitzer, a professor emeritus at North Carolina State University, noted that the results do not currently meet all established standards for the definitive identification of fossilized blood cells. She specifically questioned the relevance of the hausmannite and whether the size and shape of the structures are truly consistent with those found in living relatives of dinosaurs.

Other experts, including Timothy Cleland of the Smithsonian Institution, emphasized that while the study opens new avenues for exploring molecular preservation, it does not imply that other biological components, such as DNA, have survived. Cleland noted that heme and DNA are distinct molecules that degrade under different conditions, and further research is required to determine if such preservation is a rare occurrence or a more widespread phenomenon in the fossil record.

The research team plans to expand their investigation to other fossils from different geological periods and environments. By applying these new analytical methods, scientists hope to gain a better understanding of the physiology of extinct animals and the complex interactions between burial environments and organic degradation. This work could eventually provide deeper insights into the evolution of blood and metabolism across deep time.