What the study reports
Scientists studying a 115 million-year-old dinosaur bone say they have assembled the strongest case yet that red blood cells can survive in a fossil, according to CNN. The work was published Monday in Proceedings of the National Academy of Sciences.
The team combined new microscopic imaging with chemical analysis. It reports finding oval structures that resemble red blood cells, plus chemical evidence of heme, a molecule in hemoglobin, the protein that carries oxygen in the blood. The authors say this is the first time heme has been detected in situ, meaning inside the structures themselves, in a dinosaur fossil.
Earlier studies, going back to the late 1990s, described cell-like structures in dinosaur and other reptile fossils, but their legitimacy has been fiercely debated. Soft tissue and cells rarely survive fossilization, which is why such claims draw scrutiny.
The fossil and why it may have survived
The specimen is a partial hind limb of Aratasaurus museunacionali, a theropod from the Early Cretaceous. Paleontologists excavated it in 2008 at Mina Pedra Branca in northeastern Brazil, within the Romualdo Formation, a site known for exceptionally well-preserved fossils. Scientists believe stagnant, low-oxygen water there slowed the decay of buried remains.
Inside the bone's vascular canals, which hold blood vessels and nerve fibers, the researchers found an abundance of the oval microstructures. Lead author Kliti Grice, an organic geochemist at Curtin University in Perth, Australia, told CNN the study is distinctive because it links several lines of evidence: where the structures sit, how they look, their mineral makeup and associated chemical signals.
The team also found traces of manganese oxides, minerals it suggests may have helped stabilize and preserve the cells. The low-oxygen burial conditions, the authors propose, may have limited the breakdown of organic material.
Doubts from outside experts
Not every expert is persuaded. Mary Schweitzer, professor emeritus of biological sciences at North Carolina State University, told CNN the findings do not meet established standards for identifying fossilized blood cells. She questioned whether the shape and size of the structures match red blood cells in living relatives of dinosaurs. She also questioned the importance of hausmannite, the manganese oxide the authors mainly detected, noting that it is not found in living red blood cells.
Grice responded that the team does not regard hausmannite as an original part of the cells. In their view it formed during fossilization and may have aided preservation. The authors also noted that the structures differ in size and shape from red blood cells in living birds and crocodilians, but cautioned that modern animals may be a poor comparison for non-avian dinosaurs and that the fossil cells may have changed shape after death.
Even so, Schweitzer called the use of multiple analytical techniques an exciting advance. She said the data leave her hopeful that some of the dinosaur's own molecules remain in the bone.
What comes next, and what it does not mean
Grice said it is too early to draw conclusions about the physiology of Aratasaurus from a single specimen. A key question, she said, is whether this preservation is extraordinarily rare or has simply gone unnoticed in other fossils, possibly including specimens in museum collections. Her team plans to examine fossils from other species, time periods and environments.
If similar evidence turns up elsewhere, Grice said, it could help researchers ask far more sophisticated questions about the physiology of extinct animals. Over time, molecular clues might shed light on how dinosaurs moved oxygen through their bodies and how their biology compared with that of living animals.
Timothy Cleland, a physical scientist at the Smithsonian Institution's Museum Conservation Institute who was not involved, cautioned against Jurassic Park comparisons. Heme and DNA are different molecules that fossilize in different ways, he explained, so evidence of one does not show the other has survived. He said the study opens new avenues for exploring heme preservation in bone, especially at exceptional sites, and raises the question of whether the same preservation occurs in other animals from the Romualdo Formation.
