Researchers analysing hind-leg bones of a small meat-eating dinosaur say they have found structures that resemble fossilised red blood cells. The animal, an Aratasaurus, lived and died about 115 million years ago in what is now north-eastern Brazil. While analysing the bones, Grice spotted the structures in fine channels where blood vessels once ran.
Electron microscope images showed small, round structures in those channels. Chemical tests identified heme, the organic compound that lets haemoglobin carry oxygen, and traces of its breakdown products. Tests also found amino-acid building blocks of collagen, a protein in connective tissue. The scientists’ suspicions that they were looking at red blood cells were bolstered when those tests came back positive for heme and its breakdown products.
The claim has drawn caution. The structures are concave, and dinosaur red blood cells would be expected to show a nuclear bulge, appearing dome-like on both sides, raising the possibility they are something else. One reason for 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.
If the identification holds, it would challenge the view that endogenous organic material disappears from fossils within a million years or less and could let scientists study dinosaur blood, metabolism and activity. Schweitzer added that 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.
Schweitzer said any extraordinary claim needs extraordinary analytical evidence. She 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. The work also raises the question of what other biological material may remain in fossil collections around the world.
Researchers said fossilised red blood cells with chemistry linked to heme had not previously been found in place in any fossil, including dinosaurs. 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.