Ten years after the highly controversial discovery of soft tissue within a 68-million-year-old dinosaur bone, scientists have once again proved that we shouldn’t be so eager to dismiss exceptions to the rules, having detected what could well be red blood cells and bits of connective tissues in poorly-preserved dinosaur fossils.

This rare and exciting find suggests that our current ideas on the fossilization process may require re-evaluation and it could indicate that there is a trove of data out there that may have otherwise remained buried because scientists assumed that it wouldn’t exist. If this turns out to be the case then the discovery may usher in a new era of research, which could ultimately further our understanding of the biology of long extinct species and the relationships between them. The study has been published in Nature Communications.

When scientists discover a fossil, the vast majority of the time they’ve discovered the hard part of an animal, such as the inorganic components of bones that are made up of various mineral salts. An organism’s soft tissues, such as skin and blood vessels, generally don’t get preserved well and thus are normally absent in fossilized remains. This is because the protein molecules of which these body parts are composed decay relatively quickly, helped along by microbes that like to devour organic material. This led to the assumption that parts of proteins wouldn’t last for longer than 4 million years and that their original structure would be lost over time.

But that idea was turned on its head back in 2005 when researchers discovered soft tissue preserved inside the leg bone of a Tyrannosaurus rex. Although critics initially dismissed the find and claimed that it must be something else, scientists eventually gained support for their initial conclusion, suggesting that the presence of soft tissue could be owed to the specimen’s exceptional preservation. The latest discovery, however, demonstrates that such ideal conditions are not necessarily required for such body parts to linger in fossils for tens of millions of years.

The tissue was detected after researchers from Imperial College London analyzed eight fossil fragments from a dinosaur claw that had been housed at the Natural History Museum for over a century. Importantly, none of the specimens were exceptionally preserved. Their investigation involved the use of several different analytical methods, starting off with an imaging technique called scanning electron microscopy. By bombarding specimens with a beam of high-energy electrons, scientists could reveal information about surface structure and composition.

Next, they used a precise ion beam to cut through the samples and obtain a glimpse of the fossil’s internal structure. Finally, they used an instrument called a mass spectrometer to identify the type and concentrations of molecules present in the samples, which were then compared with samples taken from a distant relative of the dinosaur: the emu.

Through these techniques, the researchers discovered oval-shaped structures with a dense core, which they speculate could be red blood cells, although they warn that further research is needed in order to confirm this. If they are correct, this find may encourage scientists to reanalyze other specimens, which could potentially yield more red blood cells which otherwise would have gone unnoticed. And that would be a big deal, as it could allow researchers to examine how dinosaur metabolism evolved over time.

They also found fibers which exhibited the characteristic, rope-like configuration of the protein collagen, a major component of connective tissue. Since the structure of this molecule varies between species, researchers may be able to use this information to examine the relationships between extinct species, and also to gain insight into dinosaur physiology.

Sergio Bertazzo

You can check out a video of the scanning electron micrographs and 3D reconstructions from sections of the red blood cell-like structure here: