Greg Laden's Blog : The seductive siren of soft tissue preservation: Ancient dinosaur flesh wasn't ancient. Or dinosaur flesh.:
...almost.
Back in 2005, resarch published in Science claimed that blood vessels and blood cells were found inside fossil bone of a Tyrannosaurus rex.I almost feel sorry for the (YE) creationists, as they were hoping for this as some smoking gun that dinosaurs couldn't possibly be as old as they really are...
But now, researchers, in the current paper in PLoS, claim that the substance observed inside the dino bones is dried up biofilm. Bioflim is the brown yeck that forms on surfaces under water. Do you have a fish tank? That brown stuff that the snails eat. Since biofilm forms on surfaces, it can actually form the basis of an endocast ... a fossil of the inside shape of something. In addition to endocasts, mineralogical accretions can also form inside bone tissues to resemble biological tissues.
According to Thomas Kaye, one of the study's authors and an associate researcher at the Burke Museum of Natural History and Culture at the University of Washington, "I believed that preserved soft tissues had been found, but I had to change my opinion.... You have to go where the science leads, and the science leads me to believe that this is bacterial biofilm."
...almost.