It could be the opening of a Jurassic Park rip-off: scientists examining ancient dinosaur bones find what appear to be fossilised red blood cells, and traces of the molecule that gives the beast’s blood its distinctive crimson hue.

But that is what researchers are claiming to have discovered after analysing the hind leg bones of a small, meat-eating dinosaur called an Aratasaurus that lived and died in what is now north-eastern Brazil 115m years ago.

Electron microscope images of the dinosaur bones revealed small, round structures that resemble red blood cells in fine channels where blood vessels once ran, while chemical tests identified the presence of heme, the organic compound that allows haemoglobin in blood to carry oxygen around the body.

Such claims are controversial because biological tissues and molecules can break down fast, leaving little or no trace in ancient fossils. But if confirmed, it would open up entirely new avenues for scientists, allowing them to investigate dinosaur blood, metabolism and even their activity levels.

“We are seeing a mineral and molecular echo of the dinosaur’s original biology,” said Prof Kliti Grice at Curtin University in Western Australia who led the research team. “Fossilised red blood cells with distinct chemistry related to heme have never been found in situ in any fossil, let alone a dinosaur. This is a world first.”The fossilised remnants of the Aratasaurus were discovered in a mine in 2008 and have since been held in the National Museum of Brazil, where researchers continue to study them. While analysing the dinosaur’s hind leg bones, Grice spotted the structures that resembled red blood cells.

The scientists’ suspicions that they were looking at red blood cells were bolstered when chemical tests came back positive for heme and its breakdown products. Tests also found traces of the amino acid building blocks for collagen, a key protein in connective and other tissues.

If the structures really are fossilised red blood cells, as the researchers contend, it raises the question of how they were preserved. According to Grice, a manganese compound called hausmannite, which formed in and around the blood cells, may have lent a helping hand by stabilising them prior to fossilisation. The same process might have helped preserve the amino acids, she added. The study appears in Proceedings of the National Academy of Sciences.

The work is already stoking debate. Prof Mary Schweitzer at North Carolina State University in the US, who has discovered remnants of blood vessels and soft tissues in dinosaur fossils, is not convinced Grice and her colleagues have found red blood cells. One reason for her doubt is that the dinosaur’s red blood cells should have a “nuclear bulge” making them appear dome-like on both sides. The structures Grice found are concave, suggesting they might be something else.

Schweitzer was more persuaded by the discovery of heme and collagen amino acids in the bone and said there was so much more to learn from exceptionally well-preserved fossils. Schweitzer added: “The conventional wisdom in palaeontology that all endogenous organics would disappear in a million years or less is being routinely challenged, and will continue to be as technological approaches to palaeontological specimens are more routinely applied.”

Another question the research raises is what other biological material might lurk in fossils collections around the world. On this, Grice urges extreme caution, adding that her work does not imply that large biological molecules such as proteins or DNA live on in ancient fossils. “Any extraordinary claim needs extraordinary analytical evidence,” she said. “The aim isn’t to find Jurassic Park DNA, it’s to determine how much genuine molecular information deep time can preserve.”“The really exciting implication is that extraordinary molecular information may already be sitting in museum collections around the world, waiting for us to ask new questions of old fossils,” she added.