A 115-million-year-old Aratasaurus museunacionali limb bone from northeastern Brazil contains ellipsoid microstructures that researchers say are the oldest chemically supported dinosaur red blood cell remains yet identified.
Chemical mapping found iron, carbon and nitrogen consistent with heme, while laser-scattering and bone-extract tests pointed to porphyrins and heme-related compounds rather than plant contamination.
The team argues hausmannite—a manganese oxide mineral found inside the structures—may have sealed and protected the cellular traces, offering a possible mechanism for preserving blood molecules through fossilization.
Mary Schweitzer disputed that the evidence is definitive, saying the heme signals were not clearly confined to the round structures and that their size and shape do not match living birds' or reptiles' red blood cells.
If confirmed, the finding could widen efforts to recover molecular clues to dinosaur physiology and suggests this kind of preservation may be more common than previously thought.