Dinosaur fossil yields evidence of ancient blood cells

The partial leg bone belonged to Aratasaurus museunacionali, a theropod that lived during the Early Cretaceous. Paleontologists found it in 2008 at Mina Pedra Branca in northeastern Brazil, an area known for exceptionally preserved fossils. Researchers identified oval-shaped microscopic structures in the bone’s vascular canals, alongside chemical traces of heme, a component of hemoglobin that carries oxygen in red blood cells.

The study, published in Proceedings of the National Academy of Sciences, combined imaging with chemical analyses. Its authors say the work is the first to detect heme within structures in a dinosaur fossil. They also found manganese oxide minerals, which may have helped preserve the material. Low-oxygen conditions where the bone was buried may have slowed decomposition.

Some earlier studies have described structures resembling blood cells in fossils, but their interpretation has been disputed. The new findings add chemical evidence, yet researchers caution that the structures’ original identity and shape remain uncertain. One specimen is not enough to draw conclusions about the dinosaur’s physiology, and the structures also differ from the blood cells found in modern birds and crocodilians.

The team plans to investigate fossils from other species, periods and environments to learn how common this kind of preservation may be. Further research could help scientists study dinosaur biology, but the finding does not establish that DNA survived: heme and DNA are different molecules and fossilize differently. Researchers also say that whether such evidence could inform searches for life elsewhere remains a possibility, not a demonstrated result.