Ancient Blood Cells Found in 115 Million-Year-Old Dinosaur Fossil

Scientists have made a groundbreaking discovery, identifying what appear to be fossilized red blood cells in the hind leg bones of an Aratasaurus, a small meat-eating dinosaur that roamed northeastern Brazil some 115 million years ago ¹². This finding, detailed in a recent study published in the journal PNAS, marks the oldest known chemical evidence of blood-related material in a dinosaur fossil ²³.

The research team used advanced chemical tests to identify the presence of heme, the molecule responsible for the red color in blood, within the fossilized remains ¹². Additionally, they observed microscopic structures resembling red blood cells through electron microscopy, further supporting their hypothesis ¹. These structures were found inside fossilized blood vessels, adding another layer of detail to the remarkable find ³.

The significance of this discovery lies not just in the identification of these ancient cells, but also in the preservation of other organic molecules such as amino acids linked to collagen ¹. This suggests that the conditions under which the Aratasaurus was buried played a crucial role in preserving these delicate components over millions of years. One factor that may have contributed to this preservation is the presence of manganese compound hausmannite, which could have helped maintain the integrity of the cellular structures ¹.

However, not all experts are convinced. Professor Mary Schweitzer, renowned for her work on dinosaur soft tissues, expressed skepticism about the specific claim of red blood cells but acknowledged the presence of heme and collagen ¹. This highlights the ongoing debate in paleontology about the nature and extent of preservation in dinosaur fossils.

The Aratasaurus, named after the Brazilian city where it was discovered, is estimated to have been around 3 meters long and weighed approximately 34 kilograms ³. Its fossilized remains were first unearthed in a mine in 2008, providing scientists with a unique opportunity to study the internal structures of this ancient creature ¹³.

This discovery not only sheds light on the biology of dinosaurs but also challenges our understanding of how organic materials can persist over geological timescales. The larger-than-average size of the red blood cells, compared to those of modern birds and crocodiles, suggests either swelling during fossilization or a larger size in the Aratasaurus itself ³.

What we know

• - Scientists found what appear to be fossilized red blood cells in the hind leg bones of an Aratasaurus ¹²
• - Chemical tests identified the presence of heme, the molecule responsible for the red color in blood ¹²
• - The limb bones of the dinosaur contained microscopic structures resembling red blood cells ²
• - The fossilized remains of the Aratasaurus were discovered in a mine in 2008 ¹³
• - The structures resembling red blood cells were observed using electron microscopy ¹
• - Tests also detected traces of amino acids associated with collagen ¹
• - Manganese compound hausmannite may have helped preserve the structures ¹
• - The fossil belongs to a dinosaur called Aratasaurus museunacionali, approximately 10 feet long ²
• - The research was published in the journal PNAS on November 2, 2026 ²
• - Haem B, a component of hemoglobin, was detected in the cells ³
• - The red blood cells were found inside fossilized blood vessels ³
• - The Aratasaurus was estimated to be around 3 meters long and weighed approximately 34 kilograms ³
• - The red blood cells were larger than those of modern birds and crocodiles, suggesting either swelling during fossilization or a larger size in the species ³