What the researchers report
A team led by Kliti Grice, an organic geochemist at Curtin University in Perth, Australia, says it has found the strongest evidence so far of red blood cells preserved in a fossil. The study was published Monday in Proceedings of the National Academy of Sciences, according to CNN.
The specimen is a partial hind limb of Aratasaurus museunacionali, a meat-eating theropod from the Early Cretaceous. The bone is about 115 million years old. Inside its vascular canals, the microscopic channels that house blood vessels and nerve fibers, the researchers saw many oval microstructures resembling red blood cells.
Using new microscopic imaging and chemical analysis, the team reported finding heme within those structures. Heme is the part of hemoglobin that helps carry oxygen. The authors say this is the first time heme has been detected in place, inside the structures themselves, in a dinosaur fossil.
Why this bone may have survived
Soft tissues and cells seldom last through fossilization, which is why earlier claims have been so contentious. Reports of red blood cell-like shapes in dinosaur and other reptile fossils date to the late 1990s, and scientists have argued fiercely over them.
Paleontologists excavated the leg bone in 2008 at Mina Pedra Branca, in the Romualdo Formation of northeastern Brazil. The formation is known for exceptionally well-preserved fossils. Scientists think stagnant, oxygen-poor water there slowed decay of buried remains.
The authors suggest those low-oxygen conditions limited the breakdown of organic material. They also found manganese oxides in the bone, which they think may have helped stabilize the cells. The main type was hausmannite. Grice said the team does not regard it as an original part of the cells. They believe it formed during fossilization and may have aided preservation.
Where experts disagree
Mary Schweitzer, professor emerita of biological sciences at North Carolina State University, was not involved in the study. She told CNN the findings do not meet established standards for identifying fossilized blood cells. She questioned whether the structures' shape and size match red blood cells in living relatives of dinosaurs. She also questioned the significance of hausmannite, noting it is not found in living red blood cells.
The authors acknowledge that the structures differ in size and shape from red blood cells in modern birds and crocodilians. They caution that those animals may be a poor comparison for non-avian dinosaurs, and that the cells may have changed shape after death.
Even so, Schweitzer called the use of several analytical techniques an exciting advance. Based on the data, she said she is hopeful that some molecules from the dinosaur itself remain in the bone. Timothy Cleland, a physical scientist at the Smithsonian Institution's Museum Conservation Institute, also was not part of the work. He said it opens new avenues for studying heme b, the most common form, in exceptional sites. He suggested future studies could clarify how red blood cells change after an animal dies, which might explain the odd shapes.
What comes next, and the Jurassic Park question
Grice stressed that conclusions about the physiology of Aratasaurus would be premature from a single specimen. She said a key question is whether this kind of preservation is extraordinarily rare or has simply been overlooked. Museum collections worldwide may hold fossils with molecular and cellular information that no one has examined, she said.
Her team plans to study other fossils from different species, time periods and environments. If similar evidence turns up elsewhere, the authors say, it could help researchers investigate how dinosaurs moved oxygen through their bodies, how their tissues worked and how their biology compares with that of living animals.
The finding does not bring dinosaur cloning closer, Cleland said. Heme and DNA are different molecules that fossilize in bone in different ways, so evidence of one does not show the other has survived. Schweitzer added that further work on very old fossils could eventually reveal what ancient molecules say about disease, biological processes and molecular evolution.
