Researchers have detected mineralised red blood cells and heme-derived molecules inside a 115-million-year-old dinosaur fossil from Brazil, offering unprecedented chemical evidence of ancient physiology preserved within the hind limb bones of the theropod Aratasaurus museunacionali.
Aratasaurus Museunacionali and the Romualdo Formation Discovery
The fossilized remains were recovered from a mine in northeastern Brazil in 2008, originating from the Romualdo Formation in northeast Brazil, an area renowned for exceptionally well-preserved aquatic and flying reptiles. Scientists studied the partial hind limb of a small, meat-eating dinosaur known as Aratasaurus museunacionali, which lived around 115 million years ago during the Cretaceous period.
The specimen carries an extraordinary history connected to cultural loss and survival. Before researchers examined its internal chemistry, the fossil was kept in Brazil’s National Museum until a catastrophic fire destroyed much of the institution’s collection in 2018.
Microscopic Analysis and Heme B Detection
An international team led by organic geochemist Kliti Grice at Curtin University examined small bone pieces using light scanning electron microscopy, pyrolysis, and mass spectrometry. Inside tiny channels where blood vessels once ran, the team found ellipsoid microstructures that strongly resembled red blood cells.
To confirm whether the shapes were genuine biological remnants rather than modern contamination or mineral lookalikes, the researchers deployed high-performance liquid chromatography-mass spectrometry. The analysis revealed that the bone extract was dominated by heme B and related breakdown products, the iron-bearing compounds that enable hemoglobin to carry oxygen.
To detect intact heme derived molecules in 115-million-year-old red blood cells is astonishing: this really is a landmark discovery.
Kliti Grice, Curtin University
When the team analyzed the surrounding rock using the same methods, they found no heme B, detecting only signatures of chlorophyll and bacteriochlorophyll from photosynthetic microbes. Elemental mapping also showed that the cell-like microstructures correlated with iron, carbon, and nitrogen.
Microbial Mats and Hausmannite Preservation Pathways
The preservation of soft tissue across 115 million years challenges the conventional paleontological view that organic molecules break down entirely within a million years. Researchers point to the unique geological setting where the dinosaur died: it was rapidly buried in a low-oxygen environment on a microbial mat composed of bacteria and archaea.
As microorganisms fed on the carcass, oxidation combined with simultaneous mineralisation. According to the study published in the Proceedings of the National Academy of Sciences, a manganese compound known as hausmannite formed in and around the blood cells.
Scientific Debate and the Limits of Ancient DNA
Despite the advanced chemical mapping, independent experts remain divided on how to interpret the morphological structures. Mauricio Barbi from the University of Regina, who was not involved in the study, noted that identifying the shapes as red blood cells involves some interpretation, emphasizing that the team found chemical remnants and mineralised structures rather than intact, living cells.
North Carolina State University emeritus professor Mary Schweitzer, also unconnected to the research, expressed skepticism regarding the cell morphology, pointing out that non-mammalian red blood cells typically feature a nuclear bulge and are larger than the roughly 15-micron structures observed in the study. However, Schweitzer commended the multiple analytical methods used and stated that she had no problem with the presence of heme and collagen in the bone matrix.
The researchers emphasize that their findings do not point toward cloning or recovering genetic material. Tests for ancient DNA on the Aratasaurus samples came up negative. The oldest verified DNA in the fossil record belongs to a 1.1-million-year-old mammoth, leaving dinosaurs well past the threshold for genetic survival.
The aim isn’t to find Jurassic Park DNA, it’s to determine how much genuine molecular information deep time can preserve.
Kliti Grice, Curtin University
With museum collections worldwide housing thousands of unexamined fossils collected decades ago, researchers hope the discovery will encourage institutions to apply modern mass spectrometry and advanced microscopy to old specimens, opening new pathways to study the physiology of extinct animals.