Scientists are claiming the discovery of what appear to be fossilised red blood cells and traces of heme in the hind leg bones of an Aratasaurus dinosaur. This small, meat-eating dinosaur lived 115 million years ago in what is now north-eastern Brazil.
Electron microscope images of the bones revealed small, round structures resembling red blood cells within fine channels where blood vessels once ran. Chemical tests further identified heme, the organic compound that enables haemoglobin in blood to carry oxygen.
Prof Kliti Grice of Curtin University, who led the research team, stated that fossilised red blood cells with distinct chemistry related to heme have not been found in situ in any fossil before. The team also found traces of amino acid building blocks for collagen.
The preservation of these structures may have been aided by a manganese compound called hausmannite, which formed in and around the blood cells, potentially stabilising them before fossilisation. The study's findings have been published in the Proceedings of the National Academy of Sciences.
However, these claims are controversial due to the rapid breakdown of biological tissues and molecules. Prof Mary Schweitzer of North Carolina State University, while persuaded by the discovery of heme and collagen amino acids, expressed doubt about the red blood cells, noting that the structures found are concave, whereas dinosaur red blood cells should have a "nuclear bulge" making them appear dome-like.