Heme signatures in mineralized red blood cells within vascular canals of a 115-million-year-old dinosaur bone

Detection of endogenous biomolecules in vertebrate fossils remains controversial because labile compounds degrade quickly and are highly susceptible to contamination. Here, we present data on the preservation of heme-derived tetrapyrroles, and vascular canal-constrained ellipsoidal microstructures, inferred to be red blood cells, in limb bones of Aratasaurus museunacionali , a 115-million-year-old theropod dinosaur. High-performance liquid chromatography–mass spectrometry identified parent and diagenetically altered heme B as the principal tetrapyrroles of bone extract, contrasting the chlorophyll and bacteriochlorophyll porphyrin signatures of the surrounding matrix supporting an endogenous origin. Separate spatially resolved analyses by Raman spectroscopy and transmission electron microscopy confirmed the ellipsoid microstructure localization of i) porphyrin signals of heme and ii) key elements of heme (Fe, N, and C) and mineral stabilizing hausmannite (Mn ₃ O ₄ ), respectively. These results demonstrate blood-derived biomolecules in mineralized red blood cells of a dinosaur.