In 2009, the world’s most famous paleontologist made a bold claim. In “How to Build a Dinosaur,” Jack Horner proposed re-creating a small dinosaur by reactivating ancient DNA found in its descendants, chickens. His 2011 TED talk on the subject went viral. And then for the past four years, the public heard nothing.
While the Internet moved on to other viral videos and ideas, Horner and his team have been working on the “chickenosaurus” and moving ahead the science of evolutionary development. The project has already resulted in some of the first research into the embryonic development of tails.
The idea that birds are descended from dinosaurs is no longer questioned within the mainstream scientific community. Paleontologists have long studied the changes in bone structure of dinosaurs and birds over time. Meanwhile, molecular biologists have studied the composition of modern bird genes. By merging these scientists’ work, Horner, who is curator of paleontology at the Museum of the Rockies in Bozeman, Mont., hopes to answer questions about evolution.
Horner’s premise can be viewed from the launchpad of the late Michael Crichton’s novel and film “Jurassic Park,” a story that involved obtaining dinosaur DNA from undigested blood in mosquitoes preserved in amber. The idea of finding dinosaur DNA this way was taken seriously by many people, and the possibility was explored by scientists.
Jack Horner knows the “Jurassic Park” theory very well, having served not only as the inspiration for one of the main characters but also as a technical adviser for the film. But 24 years after the novel was published, we have yet to find any DNA in mosquitoes from the time of the dinosaurs.
DNA degrades under even ideal storage conditions. Cool, sterile conditions can extend its useful life to as long as perhaps a few million years, and dinosaurs disappeared about 65 million years ago. No matter how perfect a mosquito we find in a blob of amber, we cannot make a dinosaur out of that mosquito’s last blood meal.
There is only one way that DNA has been proved to survive millions of years relatively intact: by replicating itself during that time. This is exactly what happened as birds evolved from dinosaurs.
Chickens may not seem like the most obvious modern bird to convert into a dinosaur. Ostriches are the most primitive surviving species of bird. Sandhill cranes have been largely unchanged for about 10 million years. The chicks of a bird called a hoatzin have dinosaur-like claws on their fingertips that they use to climb trees before they are fledged. But ostriches, sandhill cranes and hoatzins would each be challenging to work with in a laboratory. Chickens have the advantage of being highly domesticated and easy to care for at low cost.
Working with chickens also allows scientists to benefit from decades of work that has already been done on their genome and anatomy. A massive amount of research has already been conducted on the domestic chicken due to its economic importance. Poultry science is a large field with long-established journals and entire departments at respected universities.
A genome does not evolve in a tidy fashion. Old genes are not always discarded when they fall out of use. For example, there may be a whole host of genes that direct the growth and movement of a dinosaur’s arm and fingers. If another gene evolved to fuse some of those bones into a wing during embryonic development, many of those arm-and-finger genes would be pushed to the sidelines. But the potential for a dinosaur arm could still be there. If you can identify the newer gene that causes bone fusion and disrupt its expression, those sidelined genes may suddenly start producing arms.
Horner posits that three primary engineering tasks will lead him from a conventional chicken to something resembling a miniature velociraptor (a small predator that became famous in “Jurassic Park”): creation of a long tail; the development of a toothed, beakless head; and the fashioning of arms with fingers and claws instead of wings.
The toothy snout is already here. At his lab at Harvard Medical School, Matthew Harris has made chicken embryos that express ancient genes for the growth of conical, crocodile-like teeth.
The project is considered more than an effort to make a living toy; in fact, it has the potential to affect medical research.
“We were asking, ‘What are the genetic means by which nominal features come about?’ ” Harris said.
“After 70 million years, the organism still maintains the latent mechanisms of making the beginning stages of these teeth. If that is the case, what other sort of latent potential still exists in other animals or ourselves? How does that equate to ideas about repair or medicine?”
Horner’s team will build on Harris’s work, but it will have to combine that with transgenic work, which means taking a gene from one organism and inserting it into the genome of another.
“We can do the teeth already, but birds have lost the enamel gene,” Horner said. “To make real teeth, we are going to have to do some transgenics. We are going to have to add the enamel back. This isn’t actually a very big deal to get done.”
“The hands are probably the easiest to deal with,” Horner said. Indeed, an X-ray of a chicken’s wing reveals the same bones found in the arm of a small dinosaur. All of the parts are already there.
To date, the biggest challenge in making the chickenosaurus has been the tail. Modern birds don’t have a tail beneath their feathers. Instead, they have a complicated appendage called a pygostyle, with short, fused vertebrae and connected muscles that allow them to control and fan out their tail feathers.
Turning a pygostyle back into a long tail requires learning how the pygostyle evolved in the first place. This was a question that nobody had been able to answer until recently. Horner and colleagues recently published a paper that reveals 23 different mutations that can result in fused, shortened tails among mice. In effect, they sought to mimic the history of the fossil record in a laboratory.
Bird embryos still grow dinosaur-like tails before absorbing the structure through a process known as resorbtion. Learning how to cause tail resorbtion in gecko embryos may help scientists prevent tail resorbtion in birds.
“Using genetic markers, we’ve identified what genes turn on to make certain parts and what is resorbing that particular part,” Horner said. “We are looking for what kinds of genes actually take out whole segments of tail. Our next step really is now to get ourselves a colony of [geckos] and then see if we can take some of these pathways and actually see if we can knock out the tail. . . . We’re pretty sure that the tail genes we’ve discovered in mice will work here.”
Harris is skeptical about the idea of making a chickenosaurus.
“Just because you can do an experiment doesn’t mean that you should do an experiment. What is the scientific question that is being asked? Jack is asking a question: ‘Can you remake something that was once lost?’ It is the wrong question to ask. What are you going to learn if you could do it? Technically, you are going to have a messed-up chicken. It’s not a dinosaur. It’s never going to be a dinosaur. It’s just going to be a really awful monstrosity. What we should ask is: Knowing the history of birds, what are the interesting parts of their biology that can tell us something about the dinosaurs?”
Horner disagrees about the appropriateness of making a chickenosaurus.
“I think we could achieve a suite of changes in one embryo so that the resulting animal could hatch and live out a normal life span, eating, moving and functioning without difficulty,” he said.
Horner and Harris agree that the research involved in designing a chickenosaurus could pay scientific and medical dividends. Research into factors that influence embryonic tail growth could lead to new treatments for spinal disorders. Understanding more about the mesenchyme tissue (cells that develop into circulatory, lymphatic and connective tissue) of chicken embryos that direct the growth of teeth may eventually have applications in treatment of human sarcomas, which are cancers of mesenchymal cells.
As all small dinosaurs did, the chickenosaurus would have feathers. “Jurassic Park” got that wrong, though the creator of the film’s special effects is making it up to Horner. George Lucas has funded most of the cost of the chickenosaurus project thus far, and the final price tag is expected to be relatively low.
“I’d be really surprised if we don’t have them in 10 years,” Horner said. “If we’re lucky, we’ll have them in five years. [We wouldn’t need] more than $5 million. If we did have $5 million, then we would have three different labs working on it.”
For less than the cost of the special effects for any of the “Jurassic Park” films, Jack Horner just might succeed in making a living dinosaur.
Landers is an author and freelance writer in Charlottesville.