A tiny, round mark inside the leg bone of a dinosaur from Brazil may be a fossil echo of its blood, preserved for 115 million years. Researchers say the find could help reveal how some dinosaurs lived, but other scientists caution that the evidence is not yet conclusive.
The bones belong to Aratasaurus, a small meat-eating dinosaur that lived in what is now northeastern Brazil. Its remains were found in a mine in 2008 and are now held at the National Museum of Brazil in Rio de Janeiro. Scientists led by Professor Kliti Grice of Curtin University in Western Australia examined the dinosaur’s hind leg bones using modern imaging and chemical tests.
Under an electron microscope, the team saw small, rounded structures in fine channels where blood vessels once ran. The structures look like red blood cells, the researchers report. Chemical tests also detected heme, a compound that helps the blood protein haemoglobin carry oxygen, along with products formed as heme breaks down. The team found traces of amino acids, the building blocks of collagen, a protein found in connective tissue and other parts of the body.
Grice described the results as “a mineral and molecular echo of the dinosaur’s original biology.” She said fossilised red blood cells with chemistry linked to heme had not previously been found in place inside a fossil. The study was published in Proceedings of the National Academy of Sciences.
The claim matters because biological material usually decays long before fossils are found. If the structures are truly blood cells, researchers may be able to ask new questions about dinosaur blood, metabolism and activity. Grice suggested that hausmannite, a manganese compound formed around the structures, may have helped stabilise them before fossilisation. It could also have helped preserve the amino acids, she said.
But the interpretation is disputed. Professor Mary Schweitzer of North Carolina State University, who has found soft tissue and blood-vessel remnants in dinosaur fossils, is not convinced the shapes are red blood cells. She noted that dinosaur red blood cells should have a raised center, making them dome-like on both sides. The structures in this fossil are concave, which could point to a different explanation. Schweitzer found the chemical evidence for heme and collagen amino acids more persuasive, and said new tools are challenging old assumptions about how quickly organic traces disappear.
Grice stressed that the results do not mean large molecules such as proteins or DNA survive intact in ancient fossils. Instead, the work asks how much genuine molecular information can last across deep time. The team’s finding may prompt researchers to re-examine museum fossils with newer methods, while careful testing will be needed to distinguish biological traces from other structures. As Grice put it, “The aim isn’t to find Jurassic Park DNA, it’s to determine how much genuine molecular information deep time can preserve.”