Mar 02 2020

A Claim for Dinosaur Proteins and DNA

Another paper has been published in the simmering controversy over whether or not proteins, and even DNA, can survive millions of years in well-preserved dinosaur (non-avian dinosaurs, that is) fossils. The paper looks at cartilage from a duck-billed dinosaur, a young Hypacrosaurus stebingeri. The authors claim:

“…microstructures morphologically consistent with nuclei and chromosomes in cells within calcified cartilage. We hypothesized that this exceptional cellular preservation extended to the molecular level and had molecular features in common with extant avian cartilage. Histochemical and immunological evidence supports¬†in situ¬†preservation of extracellular matrix components found in extant cartilage, including glycosaminoglycans and collagen type II. Furthermore, isolated¬†Hypacrosaurus chondrocytes react positively with two DNA intercalating stains.”

Let me say right away that these claims are controversial, but what would they mean if true? If we could examine the structure of proteins and DNA from >65 million years ago, in well-preserved dinosaur fossils, then the world of molecular biology would extend back to that era. Molecular examination has had a significant impact on paleontology – but it has limits. So far the oldest DNA sequenced from a fossil is from a 700,000 year old horse frozen in ice. The oldest protein so far confirmed is from a rhino 1.7 million years old. This means that if the current claims are true, DNA can survive in fossils 100 times longer than the current record would indicate.

This is also not the only source of information from which to estimate the lifespan of DNA. Researchers have examined DNA from Moa specimens in New Zealand, over a span of about 8,000 years. This allowed them to estimate the half-life of DNA, the time over which about half the bonds would be broken. Their estimate – 521 years. This means that all the chemical bonds in a DNA molecule would be gone after 6.8 million years, but having any fragments along enough to sequence would be gone after about one million years. This aligns nicely with the evidence from actual fossils. So claiming DNA from >65 million years would be extraordinary, to say the least. This is why most scientists remain skeptical of these claims.

The evidence in the current study is provocative, but how clear is it? The morphological evidence is at best suggestive – the microscopic structures “look like” proteins and chromosomes. This type of evidence can be valid, but is rarely definitive. It’s too easy to be fooled by wishful thinking and pattern recognition. This has lead historically to false claims, such as miscroscopic fossilized life from Mars meteorites. The staining assays are more impressive. Even without DNA, if collagen itself were preserved we could sequence the amino acids in the protein, and that can give us a molecular analysis that can be used to generate an evolutionary tree of relationships. If the DNA claims hold up, however, that would be a game-changer for paleontology.

The DNA staining used would only work on fragments of double-stranded (in one assay) or single-stranded DNA, and the second assay would not work on living cells – so not living contamination by bacteria, for example. Both assays require, therefore, at least intact DNA fragments, something that, as I detailed above, other research suggests should not be present.

The main source of skepticism is that these assays may be false positive due to contamination. The contamination does not have to be currently alive, and could have gotten into the fossil anytime in the last million years. Or there could be lab contamination. At the very least, these possibilities need to be ruled out convincingly before such extraordinary claims would be generally accepted.

But there is also another major reason for skepticism – so far the claims for very ancient (>65 million years) collagen or DNA have not been independently replicated. The last author on this study is Mary H Schweitzer, who appears to be the only one (with her collaborators) to be able to obtain such results. This is always a red flag, and until there is fully independent replication I doubt her claims will be taken seriously by the broader community. For example, in a review of this controversy in Science, we have the following representative opinions:

“I want them to be right,” says Matthew Collins, a leading paleoproteomics researcher at the University of York in the United Kingdom. “It’s great work. I just can’t replicate it.”

“It’s problematic that no other lab has been able to replicate Mary Schweitzer’s work,” says Jakob Vinther, a paleontologist at the University of Bristol in the United Kingdom, who’s tried to do so. “The idiom that exceptional claims require exceptional evidence remains,” adds Michael Buckley, a paleontologist at the University of Manchester, also in the United Kingdom.”

This is all as it should be. Scientists should be generally skeptical of such claims, and require independent replication and thoroughly ruling out the possibility of error. These are not the kinds of claims that should be accepted easily or taken at face value. Schweitzer’s story is interesting, and the Science article is worth a full read if you are interested. She does have some support among colleagues, and there are also those who feel the push back against her is amplified by the fact that she is a women and a former young-earth creationist (she was converted by the evidence while studying under Jack Horner). Some also point out that she is responding constructively to criticism by tightening her methodology to eliminate contamination.

But replication is still king, and general skepticism of her claims remains strong. I suspect that adding the claims for ancient DNA to her claims for ancient proteins will just deepen skepticism, because DNA should not not survive that long. Eventually the claims for very ancient proteins and DNA will either prove correct or fall apart. Schweitzer seems either destined for a Nobel Prize or to become a cautionary tale. I, like many others, do hope it’s the former. Extending molecular biology to the time of dinosaurs would be huge advance. But I also agree that the claims seem unlikely and we need to get beyond this replication problem.

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