Original Material Found in Triassic Reptile Fossils
The preservation of structures and original proteins in fossils has just been pushed back to the Triassic.
A new paper in PLoS One adds to the growing corpus of literature documenting soft tissue preservation in “old” bones. Two reptile species categorized as archosauromorphs (“ruling lizard shapes”) were examined by a team including Roman Pawlicki, who has argued since 1966 that original biomolecules can be preserved in dinosaurs. The specimens from Poland, a nothosaurid and a tanystropheid (aquatic and terrestrial diapsid reptiles), were analyzed multiple ways with spectroscopy, imaging, and mass spectrometry. The team photographed structures that resemble “blood vessels” (quotes theirs) preserved in iron minerals. Within the bones, amino acid residues indicative of collagen were found.
Pawlicki and the others recognize that their findings buck the conventional wisdom.
The conventional wisdom states that no original organic components remains associated with Mesozoic vertebrate bones over geological time. It is based on models using unrealistically harsh chemical conditions as proxies for time. However, half a century ago, one of us (RP) was the first to demonstrate, by describing fossilized cells, collagen fibrils and vessels from Cretaceous dinosaur bones from the Gobi Desert, that this conventional wisdom may not hold for all fossils.
The references list many previous papers assessing soft tissue in dinosaurs, including those by Mary Schweitzer, who also discussed this paper with the authors and offered suggestions. The authors wanted to be careful to refute the “biofilm” and “contamination” counter-arguments; they used a recent marine iguana bone as a control, and compared their measurements with the surrounding non-organic matrix. They also analyzed material from the interior of the bone which they reasoned is impervious to contamination.
Most of the paper goes into the weeds about their methods for preventing contamination and eliminating biofilms from bacteria or fungi. Since it’s open-access, readers can learn about how many times they soaked, blasted, irradiated and rinsed their samples. Some readers may find space for criticizing their inferences here and there (for instance, some spectra were “not completely unambiguous” for amino acids). Overall, though, the multitude of methods and cross-checks gave them confidence to conclude that original biomolecules and structures had indeed been detected.
This finding demonstrates that the possibility of the preservation of original soft tissue in iron-oxide mineral coatings may be greater than commonly believed and that molecules preserved in this way are structurally relatively undamaged and identifiable via spectral methods.
Not surprisingly, it was not their intent to cast doubt on the conventional ages, but rather to explain how they might have been preserved through deep time. Their theory is that iron oxide minerals like hematite and goethite, derived from the animal’s tissues (such as hemoglobin), provide protective coatings around the biomolecules.
Our study provides clear evidence that fossil molecules could survive through rapid, early diagenetic iron radical cross-linking. These biomolecules could effectively be preserved in iron-rich minerals when the minerals precipitated directly onto soft tissues, such as vessels and cells, and tightly covered their original structure. It can be assumed that the persistence of protein remains of endogenous origin in Early Triassic bones was the result of early post- mortem mineralization processes on the walls of blood vessels. Our observations confirm the hypothesis, that iron oxides can act as protective envelopes enabling the preservation of endogenous biomolecules in dinosaur bones from the distant geological past.
The bones, though, are dated in the paper to 247 million years old, much earlier than the dinosaurs examined by Schweitzer. That’s a long time to believe nothing happened to degrade these biomolecules completely and replace them with minerals. A lot of geological, physical and biological change can occur in just thousands of years, let alone hundreds of millions of years. To assume iron oxides protected the biomolecules, they needed the “protective envelopes” to form rapidly and then stay intact for hundreds of millions of years. That sounds like special pleading. “This phenomenon of rapid fossilization must have occurred during early diagenesis, most likely immediately after the death of the organism,” they say. Why were these reptiles, one in the water and one on land, buried rapidly? What made them fossilize immediately? How often does that happen?
We know about human history in the 103-year range, but no human has experienced millions of years. Does anyone “know” that amino acids and collagen can last that long? The syllogism relies on assuming the major premise: (1) the earth is old, (2) biomolecules are found; (3) conclusion: the biomolecules are old. What if #1 is false?
This paper may not make the strongest case, but it’s interesting and adds to the evidence. The most parsimonious explanation is that these bones were never that old. The reference list provides interested observers with resources for further investigation going back decades, including all of Mary Schweitzer’s published papers.
“Conventional wisdom” is an interesting term. It’s not often very wise. When you see the term, push on it like these scientists did and see if it falls over.