Chemical signatures in a 115-million-year-old dinosaur bone from Brazil may be preserved red blood cells, a new study suggests, but not all experts agree, Live Science reported. In a paper published Nov. 2 in the Proceedings of the National Academy of Sciences, scientists said they identified microscopic structures resembling red blood cells alongside chemical signatures of heme, the oxygen-carrying component of hemoglobin. The findings come from limb bones of a roughly 10-foot-long (3-meter) dinosaur called Aratasaurus museunacionali, a small Early Cretaceous theropod, part of the two-legged, mostly meat-eating group that includes Tyrannosaurus rex and Velociraptor. The authors said this is the first study to use chemical processes to identify heme-based signatures in dinosaur bones, though earlier work has detected blood in dinosaur fossils. "Traditionally, fossils give us information through bones, teeth, shells and morphology," the research team argued, while exceptionally preserved specimens can raise questions that anatomy alone cannot answer.
The team was not originally looking for traces of dinosaur blood, first author Grice said. Her research was driven by a broader question: how much of an ancient organism's original biology can survive fossilization. Using microscopy, mineralogical analyses, and molecular geochemistry, the researchers found numerous microscopic structures inside vascular canals, the channels that once carried blood vessels through bone. Their shape, size, and location were consistent with red blood cells, the team said. "Critically, we investigated the chemistry in situ, so we could relate the chemical signals to the microscopic structures in their physical context within the fossil," Grice said. "That is much stronger than simply extracting molecules from a piece of fossil and assuming where they originated." The analyses detected preserved heme-related compounds associated with those structures. Heme is the iron-containing, ring-shaped molecule that is a key part of hemoglobin.
The team thinks burial conditions may have helped. They suggested the animal was rapidly covered by sediment in a low-oxygen environment containing microbial mats, which may have altered decomposition. The red-blood-cell-like structures were mineralized with hausmannite, a manganese oxide, Grice said, which may have helped stabilize or replicate microscopic biological structures before they were destroyed, while some associated chemistry survived in altered form. The fossil also contained preserved amino acids associated with collagen, the structural protein in bone.
Mary Schweitzer, a molecular paleontologist at North Carolina State University who was not involved in the study but has previously studied soft tissues from the dinosaur age, was not convinced the images show remnant red blood cells. "I very much appreciate this team bringing rigor to the study of deep time fossils," she told Live Science. "I am in agreement that endogenous molecules can persist over geological time in some form." But, she said, the structures do not convincingly match the expected appearance of red blood cells in non-mammalian animals. Unlike mammalian red blood cells, which lose their nuclei, those of birds and reptiles retain a nucleus and typically show a nuclear bulge. The structures in the paper, she said, have more of a concave shape with no nuclear bulge, and were smaller than most non-mammalian red blood cells, so "morphological similarity is not met." She still praised the team's molecular approach. The verified story is a carefully argued chemical claim, and a serious, specific dissent about what the shapes actually are.