Friday, October 12, 2012

Amazing amber fossils, DNA, and Jurassic Park

Here is an amazing recent discovery: the first known fossilized example of a spider bearing down on a victim trapped in its spider web.  The spider and its victim, a male representative of an extinct genera of wasp who became entangled in the strands of web still visible and preserved, were entombed in amber, preserving the dramatic ancient scene in all its glory.

Professor George Poinar (professor emeritus of entomology at Oregon State University) and amber collector Ron Buckley recently published a discussion of this remarkable set of fossils in Historical Biology, entitled "Predatory behaviour of the social orb-weaver spider, Geratonephila burmanica n. gen., n. sp. (Araneae: Nephilidae) with its wasp prey, Cascoscelio incassus n. gen., n. sp. (Hymenoptera: Platygastridae) in Early Cretaceous Burmese amber."

Professor Poinar has published numerous studies on fossils trapped in amber, and is credited as providing the inspiration for the novel -- and blockbuster movie -- Jurassic Park, based on his success in extracting intact sequences of ancient DNA from fossil insects in amber.  

However, other scientific studies have recently provided evidence that DNA cannot survive for the millions of years that scientists ascribe to these ancient amber fossils.  This recent study of fossilized (but relatively recent) moa bones from New Zealand, some of them with some DNA intact, has caused analysts to conclude that DNA has a "half-life" of only hundreds of years (521 years, to be precise).  

This means that DNA from fossils many tens or hundreds of thousands of years old would be quite rare, while DNA should be completely degraded once fossils reach a few millions of years of age.  The scientists predicted that fossils a million years old, under ideal circumstances, might still yield some DNA, but calculated 6.8 million years as the age at which DNA would be completely gone under even the best circumstances.  The study was published in the Proceedings of the Royal Society B (Biological Sciences), an abstract of which can be seen here.  Here is a more popularly-styled discussion of the study from Wired UK.

This evidence creates a bit of a conundrum, as insects fossilized in amber -- some assumed to be many tens of millions of years old -- have yielded DNA in the past (and even apparently some living bacteria, which is a completely different conundrum).  For example, this scholarly article from 1992 entitled "DNA Sequences from a Fossil Termite in Oligo-Miocene Amber and Their Phylogenetic Implications" discusses what the authors believed to be "the oldest DNA extracted from a fossil (in 25-million-year-old amber)" (see page 1934 of the linked article).  They were able to discover DNA sequences that led to the construction of chains of base-pairs 225 pairs long from fossilized termites preserved in amber.  That should not be possible if the specimens are really 25 million years old, no matter how well amber preserved the termites!

How to solve this dilemma?  As Dr. Walt Brown, originator of the hydroplate theory, explains in his book discussing that theory (which can be read in its entirety online), this and other evidence of DNA preserved in amber fossils is not surprising at all, once scientists realize that their assumptions of great age for the amber may well be incorrect.  Dr. Brown argues that the catastrophic events surrounding a global flood led to the extremely rapid burial of some insects and spiders in masses of amber from violently ripped-apart trees, and that the amber was then rapidly buried, preserving it and its contents (see the discussion on this page of his book, particularly in figure 12). 

Dr. Brown discusses the work of Dr. Poinar -- as well as the arguments of a critic of the possibility of recovered DNA, by another scientist who claims that Dr. Poinar must have accidentally contaminated his specimens with modern DNA -- in footnotes found on this page of his book.  He writes:
Tomas Lindahl is a recognized expert on DNA and its rapid disintegration. He tried to solve this problem of “old” DNA by claiming that all such discoveries resulted from contamination and poor measurement techniques. He wrote, “The apparent observation that fully hydrated plant DNA might be retained in high-molecular mass form for 20 million years is incompatible with the known properties of the chemical structure of DNA.” [See Tomas Lindahl, “Instability and Decay of the Primary Structure of DNA,” Nature, Vol. 362, 22 April 1993, p. 714.] His claims of contamination are effectively rebutted in many of the papers listed above and by:
v George O. Poinar Jr., in “Recovery of Antediluvian DNA,” Nature, Vol. 365, 21 October 1993, p. 700. (The work of George Poinar and others was a major inspiration for the book and film, Jurassic Park.)
v Edward M. Golenberg, “Antediluvian DNA Research,” Nature, Vol. 367, 24 February 1994, p. 692.
The measurement procedures of Poinar and others were far better controlled than Lindahl realized. That is, modern DNA did not contaminate the fossil. However, Lindahl is probably correct in saying that DNA cannot last much longer than 10,000 years. All points of view are consistent when one concludes that these old ages are wrong.
The final sentence is the key.  Dr. Poinar's research and the research demonstrating the disintegration rates of DNA can both be correct, once we realize that the fossils trapped in amber (as well as the vast majority of other fossils found on our planet) are the product of a relatively recent catastrophic flood event.  Other previous posts discussing important aspects of this subject can be found here and here.  

The extremely rapid burial by a large flow of amber necessary to trap and preserve the participants in the life-and-death spider and wasp scene pictured above would certainly seem to point to a catastrophic event rather than the normal gradual processes we see around us in the modern natural world.  The huge number of such amber fossils from around the globe also speak to some ancient catastrophe (this did not happen in just one or two isolated instances).  The fact that scientists have found intact DNA inside many such fossils provides further evidence that seems to support Dr. Brown's theory -- which is supported by a host of other evidence -- for a relatively recent catastrophic flood (for blog posts discussing some of that hydroplate-supporting evidence, see here, here and here for starters).

Perhaps Jurassic Park will one day be found to be possible after all.