The finding is surprising because bone marrow is thought to decay quickly in all but the most extraordinary conditions.
But such unusual conditions may not in fact be necessary to preserve marrow, McNamara says, because the surrounding bone contains many tiny pores.
These pores are too small to allow decay-causing bacteria into the tissue. The pores also let water out while allowing in chemicals that help block decay.
The finding is "very interesting," said John Horner, curator of paleontology at Montana State University's Museum of the Rockies in Bozeman.
Horner was part of a team that in 2005 found remnants of blood vessels in the bones of a Tyrannosaurus rex.
(Read "T. Rex Soft Tissue Found Preserved" [March 24, 2005].)
In many ways, he says, the new find is similar.
"We don't know what they're composed of," he said of the T. rex fossils.
"They look like blood vessels. They're stretchy and all sorts of things, but whether they're the original substance or not, we just don't know."
(See a National Geographic magazine feature on re-creating a virtual Tyrannosaurus rex.)
"I think what they've got here is going to be a lot of fun to work on," Horner said of McNamara's finding.
The next step, McNamara says, is to determine what the fossilized marrow is made of.
"We have started the analysis, but we're not finished," she said.
The fact that part of the marrow is red, however, makes it likely that it carries some of the original biological materials, such as remnants of hemoglobin, the oxygen-carrying substance that gives blood cells their color.
But Jurassic Park notwithstanding, she finds it unlikely that DNA might have survived that long.
"The whole subject of DNA preservation in fossils is controversial," she said.
"If we get traces of protein or something, we'd be quite happy."
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