The life and times of a dinosaur may be written in its blood — if blood can be preserved in bone. Tiny microstructures found in the limb bones of a fossilized 115-million-year-old specimen are the remnants of red blood cells, researchers report November 2 in the Proceedings of the National Academy of Sciences. The team says these are both the oldest red blood cell structures yet identified and the first to be chemically proven.
But not everyone is as sanguine about that conclusion. The ability to identify such structures could offer a powerful molecular window into the physiology of long-extinct animals, including their metabolism and even activity levels, says paleontologist Kliti Grice of Curtin University in Bentley, Australia. The bone, from a fossil-rich site in northeastern Brazil called Mina Pedra Branca, belonged to the dinosaur Aratasaurus museunacionali.
Grice and her colleagues used a variety of chemical and imaging analyses to study the Cretaceous Period specimen. The team prepared thin cross-sectional slices of bone and imaged details of the limb bone’s internal structure with focused electron beams. That revealed ellipse-shaped microstructures within the limb’s fossilized network of blood vessels.
A map of the ellipsoids’ chemical element composition revealed that they were full of iron, carbon and nitrogen, all components of a biomolecule called heme. Heme is an iron-bearing, ring-shaped molecule found in hemoglobin, the protein in red blood cells that carries oxygen throughout the body. Then, the researchers used a technique that identifies molecules by how they scatter laser light.
Those analyses suggested the presence of porphyrins, ringlike organic compounds found in blood — and the precursors of heme. Finally, they ruled out contamination from other porphyrins, such as the pigment chlorophyll, by separating and identifying the molecular contents of a bone extract. That experiment also suggested heme.
Taken together, these findings point unequivocally to the preservation of molecular traces of ancient blood, the team says. They also offer a clue to a novel pathway that might preserve those traces for so many millions of years. Blood cells decompose within days of the death of an organism.
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