Molecular traces from 'blood cells' found in 115-million-year-old dinosaur bones

Coastal microbes you would find at the beach may have helped preserve red blood cells in a 115-million-year-old dinosaur fossil, a new study claims.

An international team of scientists, led by Kliti Grice at Curtin University, report they have found traces of heme, in the hind limb bones of a Brazilian feathered dinosaur Aratasaurus museunacionali.

Heme is a molecule in haemoglobin, which is a protein red blood cells use to carry oxygen.

The molecules were found inside ellipsoid structures in the vascular canals — tiny channels for blood transport — in the dinosaur bone, the researchers reported today in Proceedings of the National Academy of Sciences.

"No-one's actually found heme inside a fossil blood cell ever,"

Professor Grice said.

"It gives us a complete new type of evidence for studying dinosaur physiology, so how red blood cells connected with oxygen transport and metabolism."

The new study adds to research about preservation of dinosaur soft tissues, something once thought impossible over time periods of millions of years.

But some experts were yet to be convinced the ellipsoid shapes seen in the study were definitively blood cells. 

'No idea there would be blood'

Bones from the Aratasaurus sampled in the study were discovered in a mine in the north-east of Brazil in 2008.

The dinosaur was estimated to be about four years old, weigh 34 kilograms and measure 3.1 metres long from head to tail.

The dinosaur died on microbial mats, colonies of bacteria and archaea often found in coastal locations.

The Brazilian scientists who sent the bones to Professor Grice had no indication of what would be found inside.

Professor Grice and her team analysed small pieces of the bones using a number of tests including light scanning electron microscopy, pyrolysis and mass spectrometry.

The samples were also tested for ancient DNA but came up negative (so no-one is cloning dinosaurs anytime soon).

"They had no idea that there was going to be blood cells or heme inside," she said.

"It didn't look too special.

"What we found is that the bone was almost 80 per cent heme."

"The fact that this [fossil] was engulfed in a microbial mat probably helped enormously with this preservation," Professor Grice said.

Conditions such as oxidation as micro organisms fed on the carcass, combined with mineralisation at the same time would have preserved its soft tissue.

Blood cell status debated

Mauricio Barbi, from University of Regina, who was not involved in the study, said the authors had provided convincing evidence of mineralised structures consistent with red blood cells.

But he noted caution was still necessary.

"Their identification [of red blood cells] still involves some interpretation," Professor Barbi said.

"We are not talking about intact blood cells or preserved haemoglobin, but rather chemical remnants and mineralised structures that may retain information about the original tissues. 

"Still, that is quite remarkable considering the age of the fossil."

North Carolina State University emeritus Professor Mary Schweitzer, who was not involved in the study, said she did not think the red blood cell data was convincing.

"However, I have no problem with the presence of heme and collagen in the bone matrix," she said.

"These authors are to be commended for employing multiple methods to support their contention of endogenous 'cell-like' structures."

Professor Schweitzer said one of the images of the "cells" in the study appeared to be about 15 or so microns in size.

"This is smaller than almost all non-mammalian red blood cells, which are larger because of the retained nucleus," she said.

Soft tissue knowledge growing

While soft tissue scientists debate how to interpret the results of chemical analysis of different specimens, they agree advanced imaging techniques combined with sensitive chemical analyses are revealing hidden information in fossils.

Professor Barbi said the field was moving beyond simply asking whether biological structures could survive fossilisation to better understanding of the physiology of animals that disappeared millions of years ago.

"Ultimately, I think studies like this are opening a rather exciting window into the biology of extinct animals, even if we are still learning how to interpret what we find," he said.

Professor Schweitzer said the conventional wisdom that organic material disappeared after a million years or less was now being routinely challenged.

"There is much the past can teach us about the molecular make up of ancient organisms, their molecular evolution, and factors contributing to molecular preservation," she said.

There are hopes among researchers like Professor Grice that more museums will offer up fossils to aid this kind of research into the future.

"We'll be able to completely ask new questions of these fossils that have been in museums for decades," she said.

Curtin University researchers are also trying to understand more about the process of blood mineralising in microbial mats.

They are currently running tests on whether they can mineralise human blood with mat samples from Shark Bay.