For decades, paleontologists have dreamed of peering beyond dinosaur bones to glimpse the chemistry of the animals themselves. A new study in the Proceedings of the National Academy of Sciences is pushing that dream a little closer to reality, with what may be the strongest evidence yet of red blood cells preserved in a dinosaur fossil. The work centers on a 115 million year old theropod and raises intriguing possibilities for dinosaur biology, fossilized blood, and the surprising ways molecules can survive deep time.

The research focuses on a partial hind limb of Aratasaurus museunacionali, a theropod dinosaur from the Early Cretaceous. Paleontologists discovered the limb in 2008 at Mina Pedra Branca in northeastern Brazil, part of the Romualdo Formation. This region is already famous for its exceptionally preserved fossils, and scientists think its low oxygen, stagnant waters helped slow decomposition when animals were buried. In this case, those environmental conditions may have done something extraordinary: protect traces of ancient blood within the dinosaur’s bone.

Inside the bone’s vascular canals, which once housed blood vessels and nerve fibers, researchers found an abundance of tiny oval structures. Under the microscope, these microstructures resembled red blood cells. Visual similarity alone, however, has never been enough to convince skeptical scientists. Previous reports of red blood cell like structures in dinosaur fossils and other reptiles have sparked intense debate, partly because soft tissues and cells almost never survive fossilization and partly because lookalike mineral structures can easily mislead.

What distinguishes this new work is the combination of state of the art imaging and chemical analysis used to examine both the shape and composition of the suspected cells. The team, led by organic geochemist Kliti Grice of Curtin University in Perth, detected not only cell like forms in their original context inside the vascular canals, but also a chemical signature consistent with heme. Heme is the iron containing molecule within hemoglobin, the protein that carries oxygen in red blood cells. According to the study’s authors, this is the first time heme has been identified in situ in a dinosaur fossil, meaning within the cell like structures themselves rather than in surrounding material.

That in situ detection of heme is at the heart of why the researchers view their evidence as especially compelling. Heme is central to the function of red blood cells, so finding it bound up with the same microscopic structures that visually resemble cells and lie in the right anatomical location creates multiple, converging lines of evidence. Grice highlighted how this study integrates morphology, mineral composition, and chemical signatures not as isolated clues but as a combined argument that original biological information can survive for more than 100 million years.

The burial setting appears to have played an important role. The team suggests that low oxygen conditions at the site limited the breakdown of organic material. In addition, the bone preserves traces of manganese oxides, particularly the mineral hausmannite. The authors propose that these minerals formed during fossilization and may have helped stabilize and preserve the cell like structures and their molecular contents. If correct, it would mean the same geological forces that typically erase soft tissues occasionally help protect them, depending on local chemistry and environmental conditions.

For researchers interested in dinosaur physiology, this type of preservation could be transformative. Grice pointed out that bones already tell scientists about anatomy, growth patterns, locomotion, and evolution. Cellular and molecular preservation, however, opens an entirely different level of information. With enough examples of fossilized blood components such as heme, scientists might begin asking how dinosaurs transported oxygen through their bodies, how their tissues functioned, and how their biology compared with that of modern animals.

At the same time, the authors are cautious about how far they can go with a single specimen. They stress that it is too early to draw definitive conclusions about the physiology of Aratasaurus museunacionali itself. A key question is whether this kind of preservation is extremely rare or whether comparable traces of prehistoric blood and biomolecules have been quietly waiting in other fossils, unrecognized in museum collections around the world. I found this possibility striking, because it suggests that new techniques could turn familiar fossils into fresh sources of data.

Not everyone in the field is convinced that the structures are truly red blood cells. Mary Schweitzer, a prominent researcher in fossil soft tissues and professor emeritus at North Carolina State University, notes that the findings do not yet meet established standards for identifying fossilized blood cells. She questions whether the size and shape of the structures align closely enough with red blood cells in living dinosaur relatives such as birds and crocodilians. Schweitzer also points out that hausmannite is not present in the red blood cells of living animals, a fact that complicates the interpretation of the mineral rich structures.

The study’s authors respond that they do not interpret hausmannite as an original component of the cells, but as something that formed later and helped lock in both the structures and their chemistry during fossilization. Even with her reservations, Schweitzer describes the use of multiple analytical techniques in the study as an exciting advance. In her view, the data are encouraging for the broader effort to detect preserved dinosaur molecules and suggest that at least some original biochemical information may be present in this bone.

Another outside expert, Timothy Cleland of the Smithsonian Institution’s Museum Conservation Institute, emphasizes that finding heme is not equivalent to discovering dinosaur DNA. Heme and DNA are different molecules that fossilize differently. Evidence of one does not automatically imply the survival of the other, meaning this research does not bring science closer to a Jurassic Park style recreation of extinct animals. What it does offer is a new path for exploring how heme b, the most common form of heme, and perhaps other biomolecules might persist in exceptionally preserved sites around the world.

Cleland and others see the next step as expanding the search to more fossils from different species, time periods, and environments. That work could reveal whether the Romualdo Formation is unique in preserving red blood cell like structures or whether similar chemistry exists elsewhere. Future research may also clarify how red blood cells change after death and during fossilization, which could help explain why the Aratasaurus structures differ in size and shape from their counterparts in living birds and crocodilians.

Behind the technical details lies a broader shift in perspective. For many years, conventional wisdom held that complex biological molecules could not possibly survive for tens or hundreds of millions of years. Studies like this one are encouraging researchers to ask more open ended questions about what is truly possible. Schweitzer notes that the usability of fossil molecules preserved in deep time is only beginning to be explored, and that more work across diverse fossils will help illuminate how burial environments interact with decaying organisms.

If further evidence confirms that molecules like heme can persist in dinosaur bones, scientists may gain new tools for investigating ancient disease, metabolism, and molecular evolution. The bones that have long framed our vision of prehistoric life might also prove to be archives of original biochemistry, waiting for the right methods to reveal their secrets. In that sense, the discovery of possible dinosaur red blood cells is less a final answer and more a starting point, inviting researchers to test the limits of preservation and revisit long held assumptions about what deep time can keep.

Read more at https://www.cnn.com/2026/11/03/science/red-blood-cells-dinosaur-bone