By Will Dunham
Nov 2 (Reuters) - Scientists have discovered what they consider the strongest evidence yet of blood cells in a dinosaur fossil inside bone from the right leg of a medium-sized meat-eater that prowled Brazil some 115 million years ago during the Cretaceous Period.
The researchers identified numerous microscopic structures in bone from the species Aratasaurus museunacionali that appear to be fossilized red blood cells. They also detected chemical evidence related to a key component of
these cells — an iron-containing biomolecule called heme that is associated with hemoglobin, the protein that gives blood its red color.
The evidence for blood cells and heme was found in vascular canals inside bones of an Aratasaurus individual, thought to be a juvenile or young adult about 4 years old when it died. The bipedal dinosaur would have measured about 10 feet (3.1 meters) long.
"We have not found a vial of dinosaur blood. What we are seeing is a mineral and molecular echo of ancient biology, and that is scientifically much more interesting," said Kliti Grice, an organic and isotope geochemist at Curtin University in Perth, Australia, and lead author of the study published on Monday in the journal Proceedings of the National Academy of Sciences.
"For me, the most surprising thing is that we can see the structures together with chemical evidence of their biological origin after such enormous geological time," Grice said.
Red blood cells, continuously manufactured inside bone marrow, transport oxygen from the lungs to the body's tissues and then help bring carbon dioxide back from the tissues to the lungs to be exhaled.
Unlike hard bones and teeth, soft tissues like muscles and feathers are only rarely preserved in fossils. Cells present in bodily liquids like blood are even less commonly spotted in fossils.
"Bones and teeth tell us an enormous amount about anatomy, growth and evolution. Molecular and cellular evidence potentially adds another level of biological information," Grice said.
The research does not document dinosaur DNA, Grice said, cautioning against interpreting the discovery as evidence that intact dinosaur genetic material is present.
"DNA and other large, information-rich biomolecules have very different preservation characteristics from small molecules and chemically transformed molecular remnants. The survival of cell-like morphology and heme-related chemical signals does not mean that the DNA that was originally contained within cells has survived," Grice said.
'TESTING THE LIMITS'
The researchers also detected collagen-related amino acids in the Aratasaurus bone, though Grice noted that this is not equivalent to recovering an intact ancient protein or genetic information. Collagen is an abundant structural protein, sort of the scaffolding that holds the body's tissues together.
"What the work does encourage us to do is keep testing the limits of molecular preservation rather than assuming that all biological information must disappear after a particular length of time," Grice said.
The oldest-known DNA reported by scientists came from animals, plants and microbes dating to about 2 million years ago from sediment in Greenland.
The Aratasaurus fossil was unearthed in a gypsum mine in Ceará state in northeastern Brazil, according to paleontologist and study co-author Alexander Kellner of the National Museum of Brazil. It includes parts of the right femur, tibia and foot.
"What we believe is distinctive about the present study is the strength of the combined evidence: numerous red-blood-cell-like structures in situ within the dinosaur bone, their mineralization, their location in the vascular system, and associated in situ chemical evidence related to heme. To the best of our knowledge, that combination has not previously been demonstrated in a dinosaur fossil in this way," Grice said.
(Reporting by Will Dunham in Washington; Editing by Daniel Wallis)
