Thursday, April 21, 2005

Dinosaur vessels are *not* fresh meat

Over at The Panda's Thumb there has been some interesting fallout from the finding of blood-vessel like structures and even preserved red blood cells in a tyrannosaurus fossil. Creationists are seizing on the idea that the find contains its original components (from the living animal) to assert that the find is fresh-- i.e. Created. Dr. GH attacks the idea that the fossil contains original biocomponents, and then forcefully debunks the creationist take, in a long but very worthwhile post.

Dr. GH doubts that the microvessels contain any of the original material. Time is not kind to protein, and fossilization in particular involves rotting and maybe some higher temperatures than you'd like for preservation. Remember: fossils usually consist of just bones, with all the muscle etc long since gone. Moreover, Dr. GH points out that the scientists' methods, following recovery of the fossil, may have chemically trashed anything which may have remained. Removal of the rocky surrounds included harsh chemical treatments which may have extracted native materials. The specifics of the scientists' method were buried in the supplementary information for the paper (approximately four times the length of the maintext. Science magazine is infamous for its uselessly brief maintext methods sections) He quotes their one maintext concession to this point:

“Whether preservation is strictly morphological -- that is, just the shape is preserved; a different sort of fossil, but "just" a fossil-- and the result of some kind of unknown geochemical replacement process or whether it extends to the subcellular and molecular levels -- i.e. whether the original tissue is there-- is uncertain.” 

I have to be honest-- I'm not so sure Dr. GH is being fair here. I never went to the supplementary info, but I knew that the fossils had been extensively processed in order to expose the deeply-embedded bone vessels. I don't see any agenda in the presentation of the paper, even when told that important caveats are hidden in the Supplementary Info. When I read the caveat which I quote above, I thought they got it about right.

And their enthusiastic presentation is fully justified. Blood vessel fossils!!! It's awesome!

However, I may have benefitted from my training to be able to sense the limits of the work. For example, in the maintext they allude to having used anti-collagen antisera, which-- to a person who's never pulled a dirty blot-- might suggest preserved proteins. I just laughed. If I had a dollar for every protein blot which came up "positive..." Collagen-like molecules such as keratins from human skin are an enormous contamination headache, even in specialist labs. If they did a dot blot without a negative control, this would be a non-result that only a PI could love. Based on this sort of evidence-with-limitations, I had read the whole paper in the spirit of a "glass half full" presentation, emphasizing a positive take on the data. This is perfectly legitimate presentation strategy, although I can see that it does make it harder for an interested outsider.


The second half of Dr. GH's post is on the distortion of the data, which began with the lead scientists, got further muddied in the media, and then got willfully misrepresented on the listserves. Repeated references-- beginning with the lead authors and amplified e.g. on MSNBC-- to DNA recovery and Jurassic Park, may have led to a misunderstanding about the preservation status of the find. Dr. GH is unsparing in criticizing the whole media food chain. This is a matter for much more concern.

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