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How to Make a Dinosaur (from Chickens)
Science Fiction Precedes Science Fact: Jurassic Park and The Enormous Egg
The Jurassic Park dinosaurs in Michael Crichton’s fictional world were created by cloning DNA from dinosaur blood. In the book, ancient mosquitoes were encased in amber, containing preserved dinosaur DNA. Unfortunately, DNA is a rather fragile molecule, and degrades rather quickly, even when protected by amber. To date, a full sequence of actual dinosaur DNA has never been found. The Crichton scenario of creating dinosaurs from existing dinosaur DNA is probably not feasible. There is, however, another scenario for making dinosaurs.
In the popular children’s book The Enormous Egg by Oliver Butterworth, the young Nate Twitchell wakes one morning to discover his hen has laid an enormous egg. The egg, as it turns out, houses a Triceratops. This book is full of adventure and appeals to kids in the middle elementary school grades.
Oddly enough, Oliver Butterworth’s fictitious account of a chicken laying a dinosaur egg is not so far off from truth: scientists are currently working to create a dinosaur from chicken embryos. One day in the not-so-distant future, a chicken egg could truly hatch a dinosaur.
Jack Horner and a Revolutionary Idea
In the Badlands of Montana, paleontologist Jack Horner has studied dinosaurs for a long time. He found his first dinosaur fossil when he was eight years old. Currently, he is among the top paleontologists in the world. His publications include titles along the lines of How dinosaurs grew so large and so small (Scientific American, 2005) and Age and growth dynamics of Tyrannosaurus rex (Proceedings Royal Society, 2004).
And then there is a little article called, Typology versus transformation in the origin of birds (Trends in Ecology and Evolution 17(3):120-124, 2002).
It has long been known that birds and dinosaurs are related. The famed Archaeopteryx fossil shows a winged reptile – with feathers. The Archaeopteryx fossil has far more in common with dinosaurs than birds: it had a long, bony tail, three claws, jaws with teeth, and sharp claws on the second toe which could extend to kill prey. The animal also had wings and feathers.
The generally accepted theory is that birds are descended from a line of theropod dinosaurs known as raptors. With dinosaurs extinct and no dinosaur DNA to use in cloning applications, how else could a scientist create a dinosaur? The easiest answer to the problem would be to reverse evolution: take a bird, and turn it into a reptile.
Mutant Chicken Embryos Show Reptilian Past
By targeting certain genes in chicken embryos, it is possible to bring out the reptilian traits of the birds’ ancestors. Talpid chickens are mutants which have a lethal, though interesting, change to their developmental genes.
Talpid chicken embryos have a common set of malformations: the chicken’s limbs are generally the most affected. Scientists studying talpid chicken embryos have discovered another anomaly in the mutants: they grow teeth. Like reptiles, talpid chickens develop conical teeth, similar to those of baby alligators. Even in healthy chickens, two day old chicken embryos have 16 vertebrae. Adult chickens only have about 5 vertebrae, as the extra bones are absorbed as the chick embryo develops. By halting the absorption process, the chick would be left with a reptilian tail.
Unfortunately, talpid mutations are lethal. The chicks never develop into live animals, which presents a bit of a problem. To create a dinosaur from a bird, a genetically healthy specimen would have to be found, and specific genes manipulated to bring out the reptilian characteristics.
Birds Have Egg Teeth
The First With Wings
The first winged vertebrates capable of flight were the theropod dinosaurs. Theropods lived during the Jurassic period, approximately 200 million years ago . Some theropods were capable of flight, though some flightless (and wingless) theropods had feathers. Crocodiles are the closest phylogenic relatives of modern birds.
It is entirely possible to create a dinosaur, by manipulating specific genes in a bird’s genome. Emus are an excellent first choice, according to Jack Horner, because they have a lot of features already present to create a dinosaur the size of a Velociraptor.
The genes responsible for the majority of the reptilian vs. avian characteristics are diverse. Very pointed experiments have begun to determine if it is possible to alter the genome of a healthy chicken to obtain reptilian characteristics. Scientists Matt Harris and John Fallon, of the University of Wisconsin, used genetic engineering to induce tooth growth in a normal chicken. The experiment worked: the normal chicken embryos started growing teeth.
Beyond teeth, the genes responsible for plumage have been targeted in Chinese Silkie chickens. This breed of chicken contains scales, rather than feathers, on their legs. Harris and Fallon have been able to turn the gene for scales on and off, to create feathers on the Silkie’s scaled legs. This process can also be reversed – to turn feathered areas into scales.
Birds’ wings already contain the standard three-clawed limbs shared by dinosaurs. The claws, of course, are hidden within the wing structure. Once the gene responsible for limb vs. wing formation is understood, the process of wing formation could be halted, allowing the bird to form reptilian limbs with claws.
Essentially, once the necessary genes have all been identified, a virus could be used to target the dormant avian genes: this would allow the “sleeping” genes to turn back on (or other genes to turn off), causing a bird embryo to revert to its ancestral dinosaur form.
Shared Characteristics: Birds and Dinosaurs
Pneumatized, hollow bones
The Aerosteon had hollow bones, like modern birds
Gastroliths (gizzard stones)
Both dinosaurs and birds have gizzards, which store stones to grind food.
Genetic sequencing demonstrates modern birds are more closely related to T. Rex than to alligators
Brooding and nest building
The maiasaura (caring mother lizards) built nests and cared for their young
Jack Horner and the Chickenosaurus
Creating Dinosaurs: Should We Do It?
The moral behind the story of Jurassic Park rings loud and clear: just because we can do something, should we? There are a lot of questions which remain unanswered as research surges forward. One thing is certain: as technology advances and our ability to manipulate genetic material improves, the likelihood that someone will reverse-engineer a dinosaur increases.
Fortunately, there will be no fully grown triceratops (or, more frighteningly, a Tyrannosaurus Rex) emerging from a chicken egg. The first engineered dinosaur will likely be the size of a chicken (or an emu), and the animals are not going to overrun cities with the dramatic flair of a science fiction novel.