Traces of dinosaur blood found in world-first discovery

A 115-million-year-old fossil dinosaur bone encased in a dense mat of microbes found in Brazil contains tiny structures resembling red blood cells, and molecular traces of blood.

Along with colleagues from Brazil, Japan and the United States, we’re reporting the discovery today in the Proceedings of the National Academy of Sciences.

This is the first direct molecular evidence of compounds from dinosaur blood preserved within structures that look like red blood cells. The find offers an unprecedented window into the biology of extinct animals.

It also expands what we thought possible: that fossils can preserve soft tissues and biomolecules such as blood over millions of years.

A remarkable fossil from Brazil

We studied a fossil specimen of a small dinosaur called Aratasaurus museunacionali, found in the Romualdo Formation in northeast Brazil.

The Romualdo Formation is renowned for its exquisitely preserved fish, turtles, crocodile relatives and pterosaurs. It also contains rare dinosaur material. The site’s unique geochemical conditions have preserved fossils with fine anatomical detail rarely seen elsewhere.

Currently housed at a palaeontology museum in northeast Brazil, the dinosaur fossil consists of an exceptionally well-preserved partial hind limb.

The specimen was in Brazil’s National Museum until a catastrophic fire destroyed much of the museum’s irreplaceable collection in 2018. However, the building holding this fossil was not affected by the fire.

Its name reflects this extraordinary history. Aratasaurus combines the Tupi (an Indigenous Brazilian language) words ara (“born”) and atá (“fire”) with the Greek sauros (“lizard”). The species name museunacionali honours the museum itself.

Together, the name means “the dinosaur born from the National Museum fire”.

What we discovered inside the bone

A key question was whether the structures we saw were really biological remnants – that is, actual blood – or something that may have happened to the fossil later as the tissues were turning to stone.

Some of the most compelling evidence comes from the precise anatomical location of the structures. They are exclusively within vascular canals inside the bone – where red blood cells are found in living vertebrates.

At the same time, the sediment that surrounded the fossil didn’t have any of these structures. This makes it even less likely they came from some sort of external contamination.

We evaluated and ruled out several alternative explanations for the structures. In the end, we believe they’re most likely authentic fossilised red blood cell remains.

Chemical fingerprints of ancient blood

To further strengthen the claim, we also found two chemical “fingerprints” of blood. These had the structure of heme molecules – a key component of haemoglobin, the protein in blood which carries oxygen.

There was a dramatic difference when we analysed the chemistry of the sediment that surrounded the fossil, and the chemistry inside it. The sediment mostly contained compounds from plant and bacterial sources. The fossil bone contained a distinct signature dominated by the heme molecules.

Together, this evidence points to the conclusion that we’re seeing real preserved compounds derived from blood.

Other analysis techniques confirmed the presence of molecules from heme, as well as elements including iron, carbon and nitrogen. We also discovered amino acids associated with collagen, which is found in connective tissue.

How could this be preserved for 115 million years?

The dinosaur was rapidly buried in a low-oxygen environment which slowed down its decay. The blood did not remain fresh or unchanged. Instead, microscopic red blood cells turned into minerals during fossilisation.

Another crucial factor may be the presence of minerals such as hausmannite, which can act a bit like antioxidants. They could stabilise sensitive organic molecules and slow their breakdown.

Together, these conditions preserved biological information at a molecular level – blood and collagen – for far longer than expected.

What the cells reveal

The fossil red blood cell-like structures appear a bit larger and more rounded than the cells found in modern birds and crocodilians.

This difference may be because they were deformed as the bone fossilised. Alternatively, it could suggest the red blood cells of dinosaurs not related to birds were shaped differently than those of birds, their modern relatives.

We’ll need further research to resolve this question. However, the discovery opens intriguing new possibilities for understanding dinosaurs’ bodies at a cellular level.

How sure are we it’s really blood?

Evidence from microscopy, mineralogy, spectroscopy and molecular geochemistry all points toward the same conclusion. We are convinced these are fossilised red blood cell structures containing traces of heme molecules.

Our discovery shows that blood-derived molecules can survive for more than 110 million years under the right conditions. It also provides a plausible explanation of how it happened.

Fundamentally, it suggests soft tissues in fossils are more likely to withstand time than researchers previously thought.

Perhaps the most exciting implication is that museums around the world already hold an enormous, largely untapped scientific resource. Many fossils are not spectacular display specimens. Even so, they may preserve remarkable molecular, chemical and environmental information.

Using modern analytical techniques, we can revisit specimens collected decades ago and ask completely new questions about ancient life.

The fossil was collected and curated through the efforts of researchers including Renan Bantim and Antônio Saraiva of the Regional University of Cariri, along with Juliana Sayão and Alexander Kellner from Brazil’s National Museum and the Federal University of Rio de Janeiro, who also contributed to the research and facilitated access to the specimen. Other collaborators include Yuta Isaji, Calum Fox, Nana Ogawa and Noa Ohkouchi from the Japan Agency for Marine-Earth Science and Technology and Jasmina Wiemann from Johns Hopkins University in the US.