A dinosaur that breathed its last breath in the middle of the Cretaceous may have left behind more than a mould of its bones, with a study reporting the astonishing discovery of mineralized blood cells inside the theropod’s 115-million-year-old remains.
Claims of prehistoric chemistry persisting in fossils aren’t new. Researchers have jubilantly reported uncovering the signature of biomaterials like collagen and haemoglobin before, though not without a great deal of debate.
An international team of scientists led by Curtin University organic geochemist Kliti Grice has now identified heme – the iron-bearing component that allows hemoglobin to carry oxygen – in a fossilized Aratasaurus museunacionali leg, within a context that makes the discovery harder to dismiss as contamination.
What’s more, microscopic structures inside the limb’s hollows also contained a chemical signature consistent with the molecule, strengthening the case that the cell-like shapes may represent mineralized red blood cells.
“To detect intact heme-derived molecules in 115-million-year-old red blood cells is astonishing: this really is a landmark discovery,” says Grice. “It not only extends the known fossil record of blood, but also offers a direct molecular window into the physiology of long-extinct animals so we may better understand them and the world they lived in.”
Grice’s team examined remains recovered from the Romualdo Formation in northeastern Brazil. The roughly 3-meter-long animal was probably around four years old when it died, leaving part of its right hind limb encased in what the researchers identify as an ancient microbial mat.
Over time, even the material making up the bones and teeth ought to have dissolved away and been replaced by minerals from the surrounding rock, preserving little more than the bone’s architecture.
The possibility that any trace of the original building blocks could still be found was long considered to be dubious at best. Yet sightings of numerous rounded bodies confined to channels that once accommodated blood vessels hint at a remarkable level of preservation that begged for further investigation.
Shape alone couldn’t establish their identity, of course. Minerals and microbial growth can produce convincing cellular lookalikes. So Grice’s team combined microscopy with several analytical techniques to build the case that those shapes truly were fossilized cells that retained hints of the very same compounds that once flowed through the dinosaur’s veins.
Analysis of bone extracts identified heme B and an altered relative. That latter compound was around 90 times more abundant, indicating that most of the heme they detected had undergone a chemical change during fossilization.
Separate spectroscopy measurements revealed the signature of an iron-binding structure called porphyrin within the cell-like forms. Elemental mapping also revealed iron, nitrogen, and carbon associated with them.
It’s important to note that nature loves a good porphyrin. Plants use them to make their light-catching chlorophyll, while bacteria make similar cyclic compounds for their own functioning.
In this case, the potential dino-porphyrins were confirmed only in bone extracts, with other measurements then connecting their chemistry with the microscopic cell structures. This left open the possibility that they seeped in from the surrounding microbial mat.
The researchers point out that the mat was dominated by compounds derived from photosynthetic pigments, while the extract’s porphyrins were overwhelmingly heme-related. Taken together, this implies the critical compounds came from the fossil as opposed to its surroundings.
Claims of dinosaur blood chemistry date back to the late 1990s, following the reported recovery of heme-containing compounds from a Tyrannosaurus rex bone. A 2015 study later described possible red blood cells and collagen-like fibers in 75-million-year-old dinosaur specimens that weren’t even all that well preserved.
We have good reason to be skeptical, though. In 2019, researchers examining Centrosaurus bones found recent organic material and thriving microbial communities, illustrating how fossil bone can become a habitat with chemistry distinct from surrounding sediment.
That doesn’t mean the Aratasaurus results are unlikely. It does explain why comparisons with nearby rock cannot, by themselves, eliminate contamination. The new paper explicitly acknowledges that heme-producing microbes cannot be completely ruled out.
Other details also imply a need for caution. The purported blood cells look a little rounder and wider than those of living birds and crocodilians, for example. Of course, they may have been squished or ruptured before preservation, or dinosaur blood cells may even have had subtle differences we’re not aware of.
The researchers also detected hydroxyproline, an amino acid associated with collagen. That supports their interpretation of surviving bone-derived material, but identifying a building block is different from recovering an intact collagen protein or its sequence. The study contains no word on the protein component of hemoglobin being preserved.
A manganese oxide mineral identified in the microscopic structures called hausmannite may help explain the exceptional preservation. The researchers suggest that its antioxidant properties may have provided the material some protection.
Oxygen-poor burial conditions and microbial activity may also have contributed. This remains a proposed preservation pathway, rather than an experimentally established account of the fossil’s entire history.
The discovery is certainly one of the more compelling cases for blood-derived remnants sticking around in a dinosaur’s bones. Turning those remnants into a picture of ancient metabolism will require further work.
It’s still no Jurassic Park. But palaeontology may have just gotten a little more interesting.
The research appears in Proceedings of the National Academy of Sciences.
Source: Curtin University via Scimex
