April 30, 2016

by Laura Geggel

Apologies to people keen on reviving extinct dinosaurs, but researchers have never recovered dinosaur DNA, which is necessary for cloning. But, intriguingly, they have found fragments of mystery DNA in dinosaur bone, experts told Live Science.

It's unknown whether this DNA is dinosaurian, or whether it belongs to other life-forms, such as microbes; nondinosaurian animals, such as earthworms; or even paleontologists who have worked with these fossils.

"I've found DNA in dinosaur bone," said Mary Schweitzer, a molecular paleontologist at North Carolina State University. "But we did not sequence it — we couldn't recover it, [and] we couldn't characterize it. Whoever it belongs to is a mystery."

"That's one of the reasons that I don't work with DNA myself," Schweitzer told Live Science. "It is too prone to contamination and really difficult to interpret."

Instead, Schweitzer analyzes dinosaur fossils for soft tissue, such as the blood vessels that she and her colleagues found in an 80-million-year-old duck-billed dinosaur. But she has still pondered the steps needed to clone an extinct dinosaur. Here is the science it would take to create an actual "Jurassic Park" dinosaur, according to molecular experts.
How long can DNA survive?

Scientists need DNA to clone dinosaurs, but an organism's DNA starts decaying the moment after that organism dies.

That's because enzymes (from soil microbes, body cells and gut cells) degrade DNA. So does UV radiation. What's more, oxygen and water can chemically alter DNA, causing the strands to break, said Beth Shapiro, an associate professor in the Department of Ecology and Evolutionary Biology at the University of California, Santa Cruz.

"All of these things will break down the DNA into smaller and more degraded pieces, until eventually, there is nothing left," Shapiro told Live Science.

Still, it's unclear just how long DNA can survive.

Scientists have proposed that DNA can survive as long as a million years, but definitely not more than 5 million or 6 million years, Schweitzer said. That's woefully short of 65 million years ago, when the asteroid slammed into Earth and killed the nonavian dinosaurs.

However, more experiments are needed to determine how long, and in what conditions, DNA can survive, Schweitzer said.

Moreover, don't expect a "Jurassic Park" twist to work. In the 1993 blockbuster, scientists find dinosaur DNA in an ancient mosquito caught in amber. But amber, it turns out, does not preserve DNA well. Researchers tried to extract DNA from two stingless bees preserved in copal, a precursor of amber, in a 2013 study published in the journal PLOS ONE.

The researchers couldn't find any "convincing evidence for the preservation of ancient DNA" in either of the two copal samples they studied, and they concluded that "DNA is not preserved in this type of material," they wrote in the study.

They added, "Our results raise further doubts about claims of DNA extraction from fossil insects in amber, many millions of years older than copal." [What If a Giant Asteroid Had Not Wiped Out the Dinosaurs?]
Dinosaur DNA?

If researchers choose to study the DNA lurking in dinosaur bone, it will be difficult to say whether it was dinosaurian in nature, the experts said.

"The DNA fragments that were recovered from that horse bone were short (on average 40-ish letters long) and showed characteristic signs of postmortem damage," Shapiro told Live Science in an email. "But they could be mapped to the genome of a modern horse, and so we know that they were of horse origin."

In contrast, the dinosaurs' living relatives are birds. But birds evolved out of the theropod line — a group of bipedal, largely carnivorous dinosaurs such as Tyrannosaurus rex and Velociraptor. Other dinosaur groups — including the hadrosaurs (the duck-billed dinosaurs), the ceratopsians (such as Triceratops), the stegosaurs and the ankylosaurs — do not have living relatives.

In addition, any surviving dinosaur DNA will be highly fragmented and badly damaged.

"Here is a key problem with dinosaur DNA," Shapiro said. "I would then have to ask, 'Is this dinosaur DNA, or microbial DNA that got into the dinosaur bone while it was buried in the soil?'"
Cloning adventures

For the sake of argument, let's say that researchers found fully sequenced dinosaur DNA. This means that researchers would have an entire genome, including the so-called junk DNA and the viral DNA that's incorporated itself into the dinosaur's genetic code. This viral DNA could be a problem, especially if it could infect modern plants and animals, Schweitzer said.

Next, they'd have to find a host organism to help clone the beast. That would likely be a bird. But a mother bird is a far cry from a mother dinosaur, Schweitzer said.

"There's more to developing a vertebrate organism than just what its DNA says," she said. "A lot of the timing is dictated by genes and proteins that the mother produces during development. How is it going to get the developmental signals that it needs?"

Again, let's say that, somehow, the host mother was able to give birth to this creature. The resulting offspring would be a half-bird, half-dinosaur creation, Schweitzer said. But could this animal survive in today's climate?

"Its genes and proteins survived in a very different world," she said. "The carbon dioxide content in the atmosphere was different; the oxygen content was different; the temperatures were different — how is it going to function [in the modern environment]?" [How Do Dinosaurs Get Their Names?]

Moreover, the creature's digestive enzymes might not work on modern animals and plants, and it wouldn't have Mesozoic microbes, which it likely would need to digest and absorb nutrients, Schweitzer said.

"[Dinosaurs] were designed to break down dinosaur proteins," Schweitzer said. "Or [ancient] plants, if you want to bring a plant eater back, which I'd highly recommend."

It would be cruel to bring back just one dinosaur for our own amusement, she said. But it takes at least 5,000 animals to create a sustainable population with genetic diversity, Schweitzer said.

"How are you going to clone 5,000 T. rexes?" she asked. "And, if you could, where are you going to put them?"

There are so many problems researchers would have to overcome to clone a dinosaur, Schweitzer said. "Getting the DNA, which we have not done — that would be the easy part," she said.

Still, she plans to continue her studies on dinosaur bone. And though cloning might be a pie-in-the-sky idea, she still thinks about it from time to time.

"To be honest, I'd really like to see a T. rex," Schweitzer said. "It would be very cool."