continues, with a long article in Wired magazine this week exploring the issue. The Wired reporter, Evan Ratliff, takes a refreshingly skeptical view through much of the article. It's a good read, and I recommend it.
But first, an update on the science: Mary Schweitzer, John Asara and colleagues published a new report in Science on May 1 describing their analysis of an 80-million-year-old fossil from the dinosaur Brachylophosaurus canadensis, a hadrosaur that is 12 million years older than T. rex. Once again, they found fragments from collagen, the protein that is a major component of bone, and as with their original T. rex study, they claim that these represent original dinosaur proteins. And as before, they found that the dinosaur proteins most closely resemble modern birds – in particular, ostrich.
The new study spends a significant amount of effort addressing the question of contamination. This question has been raised in at least two ways. Tom Kaye and colleagues reported in PLoS ONE that the soft tissue found by Schweitzer could be explained as a bacterial biofilm, rather than as preserved dinosaur tissue. I still like the biofilm explanation, and I don’t see how the new study refutes it. The study contains many microscope photos showing how the fine structure of the fossilized bone resembles modern ostrich bone, but preserved physical structure is not in question. The real question is, did dinosaur proteins survive for 80 million years in these bones?
The second contamination question emerges from this: Marty McIntosh discovered – after Asara released his mass spec data to the public – that the original T. rex sample contained hemoglobin. This finding has been discussed in the mass spec community, and privately among a group of scientists (including me) following this story, but it has not been published (as far as I know) until the Wired article.
Hemoglobin! Now, from what I know, we don’t expect to find much hemoglobin in bone tissue, and we sure don’t expect to find it in 68-million-year-old fossils. Could this be another big discovery? Or could it, perhaps, be that the sample is contaminated with modern proteins, perhaps from ostrich?
Upon further inquiry, a number of scientists learned that John Asara’s lab had indeed used its mass spec equipment to analyze samples of ostrich bone. Asara reports (in the Wired article) that the ostrich sample had been analyzed long before either of the dinosaurs:
“Asara conducted his ostrich and T. rex experiments a year and a half apart, separated by roughly 1,500 mass spectrometry runs. According to Asara, none of those spectra, nor samples of the soil surrounding the fossils, nor his daily control runs—in which he sequences known solutions to check for contaminants—turned up any ostrich hemoglobin.”The new Science paper on the hadrosaur proteins doesn’t mention the (unpublished) hemoglobin fragments in the T. rex data, so this important question was not addressed. Well, if Asara’s lab handled ostrich material, then I remain skeptical of their assurances that ostrich couldn’t have possibly contaminated the original T. rex samples. And Marty McIntosh explained to the Wired reporter that “a chemical modification on the hemoglobin makes it more likely to be contamination.” McIntosh submitted a paper on his results to Science, but they rejected it – perhaps because it called into a question a finding that Science’s editors have obviously endorsed. That’s too bad.
If the T. rex sample was contaminated, that throws all the results into question. It also throws into question the new hadrosaur results – if contamination was a problem before, it might be still. The best way to resolve this is for an independent group to take the original fossils and repeat the study. I know that there are groups trying to do exactly this, but the fossils are controlled by paleontologist Jack Horner, who thus far has refused to share them with anyone but Schweitzer.
Extraordinary claims require extraordinary evidence, as any good skeptic knows. The finding of intact collagen protein in dinosaur fossils is certainly an extraordinary claim, and the finding of hemoglobin is even more stunning. Alas, the alternative explanations (statistical artifacts - see my earlier blogs and Pavel Pevzner's article in Science - and contamination by bacteria and/or ostrich tissue) are much more likely. I'd love for these results to be true - intact dinosaur proteins! Think of all the evolutionary comparisons we could do if we can reconstruct the past 80 million years directly from the molecular record! But I'm afraid I remain skeptical.