A dinosaur leg bone that has been in museum collections since 2008 may contain the oldest chemical evidence of blood ever found in a fossil. In a study published Nov. 2 in the Proceedings of the National Academy of Sciences, an international team reported tiny, cell-like structures inside the bone's blood vessel canals along with heme B, the iron-bearing molecule that lets red blood cells carry oxygen.

The bone belongs to Aratasaurus museunacionali, a meat-eating dinosaur that lived about 115 million years ago in what is now northeastern Brazil. If confirmed, the find pushes the candidate record of dinosaur blood cells back by roughly 35 million years. Not everyone is convinced, and the team itself says the next step is replication.

A Bone That Waited Years for a Second Look

The fossil was dug from a gypsum mine in Ceará state in 2008. It includes parts of the right femur, tibia, and foot of a juvenile, about 4 years old, that would have measured roughly 10 feet (3.1 meters) long. The species was formally named in 2020.

According to Agência Brasil reporting, the specimen went first to a paleontology museum in Santana do Cariri, then to the National Museum of Brazil in Rio de Janeiro. It survived the 2018 fire that destroyed much of that museum's collection. Its name honors the institution.

The new work was led by Kliti Grice, an organic geochemist at Curtin University in Australia. Co-authors include paleontologist Alexander Kellner of the National Museum of Brazil.

Ellipsoidal Shapes and a Chemical Fingerprint

Under the microscope, the team found many small, ellipsoidal structures packed inside the bone's vascular canals, where blood once flowed. "When we examined the Aratasaurus bone at the microscopic and chemical level, we encountered structures that were remarkably cell-like," Grice told ScienceAlert.

Shape alone proves little — which is why the chemistry carries the claim. Using high-performance liquid chromatography and mass spectrometry, the researchers found the bone extract was dominated by heme B. Elemental maps showed iron, carbon and nitrogen concentrated on the cell-like structures, while the surrounding bone held mostly phosphorus, calcium and fluorine.

According to New Atlas, an altered form of heme was about 90 times more abundant than intact heme B. That suggests most of the original molecule changed chemically during fossilization, which is what scientists would expect over such a span.

The team credits an unusual burial for the preservation. The animal appears to have settled into a shallow, nearly oxygen-free setting covered by microbial mats. A manganese oxide mineral called hausmannite then coated the structures, acting like a natural time capsule, according to a Curtin University release.

The Contamination Checks

The biggest threat to any claim of ancient biomolecules is contamination from microbes, groundwater or modern handling. The researchers say they looked for the usual impostors and did not find them.

They reported no microbial filaments, spores or biofilms that could mimic cells. They found no pyrite crystals or sediment grains of similar size. Most importantly, the surrounding rock told a different chemical story: it carried signatures of chlorophyll and bacteriochlorophyll from photosynthetic microbes, but no heme B. That contrast suggests the heme came from the bone rather than the burial environment.

The team also detected amino acids associated with collagen. Grice was careful about the limits. She told Reuters the work is not "a vial of dinosaur blood," and she has said the findings do not mean dinosaur DNA survived.

Skeptics Say the Shapes Do Not Fit

The debate centers on whether the structures truly are red blood cells. Mary Schweitzer, a molecular paleontologist at North Carolina State University who was not involved in the study, welcomed the chemical approach but disputed the interpretation. "I am not convinced that the images they figure are remnant RBCs," she told Live Science.

Schweitzer noted that red blood cells in birds and reptiles, the dinosaurs' closest living relatives, carry a nucleus that creates a bulge. The Aratasaurus structures appear concave, with no bulge, and are smaller than most non-mammalian red blood cells. Her own team has reported heme in Tyrannosaurus rex and Brachylophosaurus tissues using different methods.

The evidence picture, then, is mixed. This is a peer-reviewed laboratory study of a single specimen, published in a major journal. It found strong chemical evidence of heme associated with cell-like structures. It did not prove those structures are intact red blood cells, and it did not recover proteins or DNA in usable form. "The immediate priority is replication," Grice said.

Past claims have shown why caution matters. A 2015 study described possible red blood cells and collagen-like fibers in 75-million-year-old specimens, and earlier claims of dinosaur proteins have been difficult to repeat.

For readers, the practical meaning is less about dinosaurs walking again and more about what museum drawers may still hide — specimens collected decades ago can yield new data as tools improve. If other labs confirm the heme signal in independent samples, the technique could help scientists study how dinosaur metabolism and activity levels evolved.

Grice has framed the work as a reason to keep probing deep time rather than a final word. She told Reuters the study encourages scientists to "keep testing the limits of molecular preservation" instead of assuming all biological information disappears after a set number of years.

The next steps are replication on additional Aratasaurus material and on other fossils from the same Brazilian deposits. Until then, the find is best described as the strongest chemical case yet for dinosaur blood remnants, not a settled answer.

What Readers Want to Know

What did scientists find in the dinosaur bone? Small, cell-like structures inside blood vessel canals and heme B, the iron-containing part of hemoglobin.

Which dinosaur was it? Aratasaurus museunacionali, a meat-eating theropod that lived about 115 million years ago in northeastern Brazil.

Is this real dinosaur blood? Not liquid blood. Researchers describe mineralized structures and chemical traces. Some experts doubt the structures are red blood cells.

How did researchers rule out contamination? They found no microbial structures or mimicking minerals, and the surrounding rock lacked heme B.

Does this mean dinosaur DNA survived? No. The lead researcher said the findings do not show that DNA was preserved.

What happens next? Other teams will need to replicate the results on more samples before the claim is widely accepted.