Inside a limb bone from a small theropod in northwestern Brazil, researchers found mineralized red blood cells—and chemical traces of what made them blood. The cells belonged to Aratasaurus museunacionali, a dinosaur that lived about 115 million years ago.
The discovery, led by Curtin University researchers, offers unusually direct evidence of how ancient animals’ tissues were built. Fossils often preserve bones and outlines, but the molecules inside them are far more fragile. Earlier studies had described shapes that might have been red blood cells. This team says it has chemically confirmed heme, the oxygen-carrying part of hemoglobin, inside cells preserved in the dinosaur’s bone. The researchers also detected amino acids from collagen, a key protein in connective tissue.
The findings were published in the Proceedings of the National Academy of Sciences. The team found numerous cell-like remains within vascular canals, the small channels that carry blood through bone. Mineral called hausmannite had formed around the cells. The researchers say it helped protect their structures and molecular traces over deep time, acting like a natural time capsule.
The scientists think the bone’s preservation began soon after the dinosaur died. Their explanation is that it was quickly buried in a low-oxygen setting rich in microbes. Those conditions, together with the mineral coating, may have limited damage and helped preserve traces that researchers had thought were unlikely to last so long.
Lead author Kliti Grice, founding director of Curtin’s WA-Organic and Isotope Geochemistry Centre, called the result “a landmark discovery.” She said finding intact heme-derived molecules in 115-million-year-old cells extends the known fossil record of blood and gives scientists a molecular way to study long-extinct animals. Such evidence may help researchers investigate how blood and metabolism evolved, and perhaps learn more about how active ancient animals were.
The work brought together researchers from Curtin University, the Japan Agency for Marine-Earth Science and Technology, Brazil’s National Museum and Regional University of Cariri, and Johns Hopkins University. That mix of expertise helped the team connect the fossil’s chemistry with the conditions that may have preserved it.
The result may also matter beyond paleontology. Martin Van Kranendonk, head of Curtin’s School of Earth and Planetary Sciences, said the research could inform astrobiology, the study of the possibility of life beyond Earth. If fragile molecular traces can survive for millions of years under the right conditions, scientists may have new clues about what to look for in ancient rocks on Earth—and, potentially, elsewhere.
For now, the Brazilian dinosaur bone shows that fossils can hold more than shape and stone. The researchers’ next challenge is to test how often minerals and burial conditions preserve such traces, and what those molecules can reveal about life that vanished long before humans appeared.