Dinosaur Soft Tissue: Fooled by Slime?

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Posted on July 30, 2008 in Dinosaurs, Fossils

The claim made in 2005 that soft tissues in dinosaur bone had been discovered (see 03/24/2005) has been challenged by new research published in PLoS One.1  Maybe the pliable stuff is just slime.
    Thomas Kaye from the Burke Museum of Natural History in Seattle with two colleagues were actually hoping to find more soft tissue samples.  After analysis, they concluded instead that what they saw in both dinosaur bone, turtle and ammonite fossils is bacterial biofilm that grew in the hollow spaces inside the fossils.  This challenges the findings of Mary Schweitzer’s team who not only claim to have found flexible tissues and remnant blood vessels, but had also sequenced collagen protein in the samples (04/12/2007).  Kaye interprets the putative iron-rich blood cell remnants as framboids – microscopic mineral spheres.  Finding similar structures in an ammonite (squid-like animal with a shell) and turtle indicated to the team that these framboids were too common to be examples of exceptional preservation from the original tissue.  Instead, they postulate that bacterial biofilms grew inside and around the original tissue, maintaining the shape of it after it had decayed away.  The paper was summarized by Science Daily, PhysOrg and Reuters.
    According to New Scientist, though, Schweitzer is not convinced.  Her studies indicated that the dinosaur collagen resembled that of chicken, and the mammoth collagen resembled that of elephants.  Kaye offered no explanation for how that could happen, she said.  Other scientists quoted in the article conjectured that the tissues could be composites of both original tissue and biofilm.  The Reuters article quotes Kaye as saying, “We are not experts in the field.  We are not disagreeing with the fact that their instruments detected protein.  We are offering an alternative explanation.”
    The original paper offered more evidence that the proteins are from modern bacteria:

Bridged trails observed in biofilms indicate that a previously viscous film was populated with swimming bacteria.  Carbon dating of the film points to its relatively modern origin.  A comparison of infrared spectra of modern biofilms with modern collagen and fossil bone coatings suggests that modern biofilms share a closer molecular make-up than modern collagen to the coatings from fossil bones.  Blood cell size iron-oxygen spheres found in the vessels were identified as an oxidized form of formerly pyritic framboids.  Our observations appeal to a more conservative explanation for the structures found preserved in fossil bone.

The team investigated 15 genera from seven different geological formations, including the Hell Creek formation where the T. rex soft tissue had been found.  The tissues in this investigation were compared with modern biofilms grown in the laboratory.  Some of them bore branching structures mimicking blood vessels.  The procedure, however, is not as simple as just looking at the tissue with a magnifying class.  Their methods indicate significant alteration and interpretation:

A turtle carapace from the Hell Creek formation was selected for spectroscopy because of its proportionally large chambers in the trabecular bone that allowed scraping the coatings loose.  Two milligrams of material was ground with 450 milligrams of potassium bromide (KBr) and pressed into a pellet using 8 tons pressure.  Modern biofilms grown on microscope slides in pond water were allowed to desiccate for 7 days and 2.5 milligrams were pressed into a KBr pellet as above.  A 2.5 milligram sample of desiccated tendon from a chicken was ground with KBr and pelletized.  Spectrums were taken on a Nicolet 510P bench at 1 cm–1 resolution with a minimum of 15 scans.  Infrared flux was matched within 5% for all specimens and a clean KBr pellet used for background subtraction between specimens.  Excel cross correlation routines were used to determine percentage of similarity for spectrums.

The team did apply several cross-checks.  Bones from the surface and from burial meters down showed the same effects.  Spectra from living and fossilized specimens were compared.  They did not find as close a correlation of the tissues with modern collagen—only 37%.  In addition, the radiocarbon dates correlated with modern times.
    How did these biofilms grow to look so much like original soft tissue?  Here was their explanation:

A biofilm would coat the voids of vascular canals and lacunae, producing an endocast of the structure.  Once the bone is dissolved, these biofilm endocasts would closely mimic pliable vascular structures.  The results presented here suggest that the tubular structures and osteocytes are formed by this process.  The lack of observed cell structure in the transparent tubes is inconsistent with preserved tissues.

They further stated that bacteria are known to produce collagen-like proteins.  And since biofilms are ubiquitous in nature, existing on almost any water/surface boundary, they could be expected in the cave-like surfaces inside bones.  “They provide a protective medium against changes in the broader environment from pH levels, toxins, etc.,” they said.  “They are viscous, flexible and long lasting through mineralization.”  That’s how the earlier team was misled, they think: “When biofilms coat a substrate, and that substrate is subsequently removed, the biofilm will retain much of the original morphology.  This can explain the quantity and similarity of structures found in fossil bone and indicates that these structures are unlikely to be preserved dinosaurian tissues but the product of common bacterial activities.
    It appears, therefore, that they made a good case for interpreting the soft tissues as modern bacterial slime, not original dinosaurian remnants.  Further investigation will be required to answer new questions this interpretation raises – along with time for rebuttal from the Schweitzer team.
Update::  After our first posting of this story today, National Geographic reported it and said Mary Schweitzer is standing by her claims.  She offered four counter-arguments: (1) No biofilms have been reported with branching, hollow tubes such as the ones she found in the T. rex bone; (2) Over time, gravity would have made the films thicker at the bottom, contrary to what her team found; (3) Methane-breathing bacteria have never been reported inside bone; (4) Kaye’s team failed to address her team’s follow-up reports that employed chemical and molecular evidence for soft tissue.  Surprisingly, Kaye responded, “If they say they got T. rex protein, then we’re not disagreeing.”  He just questioned why they got so little of it.  A paleontologist at the National Museum of Natural History left it as a draw.  Both teams make compelling arguments.  “I think you do have two very interesting alternative hypotheses,” he said.

1.  Kaye, Gaugler and Sawlowicz, “Dinosaurian Soft Tissues Interpreted as Bacterial Biofilms,” Public Library of Science One 3(7): e2808 doi:10.1371/journal.pone.0002808.

We agree with Kaye that “You have to go where the science leads,” and if Schweitzer ever retracts the claim (based on the best evidence and further study) that these represent (at least in part) original soft tissues from the dinosaur, then so be it.  We’ll have to concede the point.  However, a number of questions arise from the new interpretation.  For one thing, as some observers noted in the New Scientist write-up, the structures could still be a composite of original tissue and biofilm.  And why did Schweitzer get a match of collagen in the dinosaur bone with that of chickens, while using the same techniques, got the collagen in mastodon bone to resemble that of elephants?  What about Schweitzer’s discovery of fragile medullary bone in the same dinosaur fossil? (see 11/11/2006).
    We asked a dozen follow-up questions in the 11/11/2006 entry when the slime interpretation was first raised.  More questions come to mind now.  Why was biofilm inside fossilized bone discovered now, after centuries of collecting fossils?  Is there something in common with the environments displaying this phenomenon?  What did all the scraping, grinding and pressing do to the original material?  Maybe less destructive techniques need to be used for corroboration.  Even if biofilms can conform to original tissues and persist after they decay away or fossilize, is it reasonable to believe they would remain unaltered for 68 million years?  If the biofilms date modern by radiocarbon methods, and bacteria are still seen swimming around, it would have to imply the bacteria have been sitting there all this time, incorporating carbon-14 as they grow and divide millions of times.  What did they live on after the original tissue was all gone?  Wouldn’t there be evidence of millions of generations of biological growth in the bacterial colony?  How reasonable is it to assume that for 68 million years, a biofilm would maintain such a good mimic of original dinosaur tissue (now long gone) that it would fool careful researchers in the lab?
    So even granting victory to the Kaye team’s interpretation would seem to still argue these bones aren’t that old.  Evolutionists tell us the world underwent drastic changes since this fossil was deposited.  A meteor nearly destroyed all life on earth.  Mountains rose, valleys sank, floods came, tectonic plates mashed against one another while others drifted apart, climates warmed and cooled, ice sheets blanketed continents and animal life was evolving like crazy.  Cows evolved into whales and shrews evolved into giraffes.  All that time, we are asked to believe, the bacteria in that bone held hands to maintain the shape of long-gone soft tissue for millions of generations, till in 2005 a team of scientists found it so perfectly matching collagen and blood vessels they announced to the world the discovery of original soft tissue.  How credible is that?  The fact that Kaye et al found similar biofilms in ammonite and turtle might just suggest those fossils aren’t millions of years old, either.
    This is a scientific controversy in progress.  It illustrates the tentative nature of scientific announcements.  The biofilm advocates might argue that Schweitzer’s soft-tissue interpretation is the extraordinary claim that demands extraordinary evidence.  One should take a conservative, guarded attitude about it till more observations can test it.  Fine; creationists were going strong without dinosaur soft tissue.  Their views do not require it.  It would be very interesting to them if the soft-tissue interpretation wins out, and they could employ it as additional evidence falsifying millions of years.  Even so, their claims were no less robust before the surprise announcement in 2005.  Creationists don’t need the soft tissue, but evolutionists need their millions of years.  As we have argued, the biofilm interpretation, even if it wins out, does not get rid of their difficulty.

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