In 2005 the unexpected occurred; researchers reported what appeared to be preserved soft tissues inside the femur of a Tyrannosaurus rex excavated from the Hell Creek Formation. Structures that looked like blood vessels and blood cells were seen under the microscope, and although it is still unknown whether this is original organic material or material that has somehow been preserved the structures provided some tantalizing clues. What the researchers have been more confident about, however, is that they were able to detect the presence of preserved collagen proteins in the material. (Indeed, research carried out in 1999 on the remnants of feathers of Shuvuuvia illustrated that proteins have the potential to survive over tens of millions of years.)
In a Science paper published last year it was announced that the proteins most closely matched those from chickens supporting the notion that ancient proteins can be preserved in the fossil record. A short communication published just this past spring again confirmed the 2007 protein test results (although the phylogenetic tree that was produced lacked resolution), and a 2007 report published in the Proceedings of the Royal Society B suggested that such preservation of soft tissues might exist even from Triassic bones. There may be plenty of previously unseen treasures in bones stored in museums.
Now along comes a new PLoS paper that brings all these announcements about Tyrannosaurus soft tissue into question. Sampling a variety of genera from Hell Creek and elsewhere, researchers hypothesize that the structures that look like blood vessels and cells from the famous Tyrannosaurus femur are really just biofilm, slimy accumulations of bacteria that oozed into the bone and took the shape of the structures. What’s more, the published data from the Tyrannosaurus protein studies showed the presence of at least some bacterial contamination, and the authors of the PLoS paper suggest that the bacteria might have contained collagen-like proteins and therefore made the findings of the earlier studies ambiguous. The question is whether this new paper is going to stand up to scrutiny.
Does this new paper sound the death knell for ancient dinosaur proteins? Certainly not. It is a new alternative explanation that offers up a hypothesis and should be treated with scrutiny (just as any other paper). The analysis of the proteins said to have been taken from the Tyrannosaurus material published last year have been criticized, as well, so there’s definitely still room for debate here.
As Jerry Harris aptly noted in a comment on this subject over at Aetiology the new PLoS paper primarily looks at morphology of the bacteria rather than the biochemistry of it, thus putting it more at odds with the 2007 survey of potential preserved soft tissues than the analysis of the proteins. It’s like judging how good a wine is by beer criteria; one doesn’t necessarily contradict the other. I’m sure more papers will be published about the potential Tyrannosaurus proteins but until then it would be foolish to say that the preserved structures are “just biofilm” or to unquestionably accept that the material really is preserved Tyrannosaurus goo. More work needs to be done, and I certainly look forward to seeing how molecular biology and paleontology come together over the coming years.