Test Tube Dinosaurs
Dinosaurs – the giant primeval beasts have fascinated old and young for a long time. Michael Crichton’s and Steven Spielberg’s Jurassic Park has inspired fantasies that, maybe one day, we might be able to see them in real life. In the movie, scientists used blood from fossilised insects that were once sucking on T-rex and Co to extract dinosaur DNA to bring them back to life.
However, scientists have now shattered hopes that we will be buying our first Jurassic Park tickets any time soon. An Australian research team concluded that DNA would not survive longer than 6.8 million years. A pretty impressive time span; however, dinosaurs first appeared around 230 millions of years ago, and died out almost 70 million years ago.
The international research grouped examined 150 leg bones of the moa, a giant extinct bird. The bones were about 600-8,000 years old and collected from three different sites.
Palaeo-geneticists led by Morten Allentoft at the University of Copenhagen and Michael Bunce at Murdoch University in Perth, Australia found that the half-life of DNA is 521 years. This means that, half of the DNA bonds would have broken after 521 years; 1042 years later another half of the remaining bonds would have decayed; and so on.
DNA has a limited “life span”, or more accurately, chemical stability. Without the repair mechanisms of a living cell, DNA decays and is eaten by micro-organisms. This is also influenced by environmental conditions such as temperature, humidity or oxygen levels. “Other factors that impact on DNA preservation are clearly at work,” Bunce tells Nature news. “Storage following excavation, soil chemistry and even the time of year when the animal died are all likely contributing factors that will need looking into.”
“This confirms the widely held suspicion that claims of DNA from dinosaurs and ancient insects trapped in amber are incorrect,” says Simon Ho in Nature news, a computational evolutionary biologist at the University of Sydney in Australia.
Even if DNA fragments were theoretically retrievable from more than 1 million year old bones (if stored at -5°C), DNA pieces would be too small to contain any useful information, and after 6.8 million years, would be completely destroyed. This makes finding intact DNA from around 200 million years ago, the “prime time” of dinosaurs, very unlikely.
Ho, however, remains, optimistic, telling Nature news that “We might be able to break the record for the oldest authentic DNA sequence, which currently stands at about half a million years”.
In fact, a recent study has analysed bones cells (osteocytes) of two dinosaurs, Tyrannosaurus rex and Brachylophosaurus canadensis. They claim to have found remnants of bones cells (osteocytes), which could contain DNA. This remains yet to be verified; and even if the cells contained DNA, there may not be enough left to confirm its origin. Osteocytes are “invincible” and cannot be destroyed by other cells, and thus, could be preserved in ancient tissue.
Dr Mary H Schweitzer, lead author of bone cell study, stated: “Allenthoft and collegues used their data to propose, essentially, a MODEL for DNA degradation, based upon extrapolating the data they gathered. They also say that in many cases the DNA preservation cannot be correlated to age”.
“Models are hypotheses, and they put forth a prediction. These authors did not test fossils dating back older, rather predicted that DNA would be gone–single bases–by a certain time point”.
“We have data that does not support their hypothesis. We have 4 independent lines of evidence that there is material chemically consistent with DNA in a single punctate location within the interior of ‘cells’ that are morphologically consistent with bone forming cells of other vertebrates. That seems to indicate a measurable amount of a molecule consistent with DNA”.
“It is very important to stress that without sequence data, it isn’t really informative. We cant’ demonstrate that the reactive material inside these dinosaur ‘cells’ is dinosaur DNA without sequence. But it is hard to posit that it is a contaminant because of the localization, and the pattern is inconsistent with microbial (in the supplemental info) and the identification of histone sequence rules out microbial contamination. At this point, it is most parsimonious to conclude, based upon the existing data, that there is a small remnant of vertebrate DNA localizing to these structures, and until someone shows how contamination with human or other DNA can result in such punctate localization, it is most parsimonious to assume it is original”.
She adds: “The problem with models and estimates such as presented in the Allentoft paper is that it inhibits further investigation. If you “know” DNA can’t persist, then why should you (and why should anyone fund) look for it in older fossils? And if you don’t look you won’t find”.
DNA decay rates slow down with decreasing temperature. Maybe somewhere in the arctic regions there is a dinosaur with intact DNA waiting to be discovered. Until then, cloning dinosaurs remains a subject for Hollywood and science fiction.