In How to Build a Dinosaur, well-known paleontologist Jack Horner and co-writer James Gorman set the stage for a bold proposal, although it's not quite as bold as the title would suggest. The lineage from dinosaur to bird is pretty well accepted. As more evidence is collected and analyzed, the bird-dinosaur linkage gets stronger all the time.
Horner proposes a new direction in evolutionary research—the developmental modification of a chicken embryo to create animals with primitive dinosaurian characteristics such as teeth, long tails, and clawed forearms instead of wings.
Molecular Paleontology
The first three-fourths of the book are a recapitulation of the discoveries and events that ultimately lead to Horner's thoughts on how to build a dinosaur. For those who have kept up with dinosaur research over the past several years, it's bit of a replay. But what an interesting replay it is.
The surprising discovery of soft flexible tissue and the appearance of what look like blood cells and the remnants of vessels in fossilized Tyrannosaurus bones are surely among the most tantalizing bits of data yet obtained in vertebrate paleontology. Evidence for the existence of ancient collagen (a common animal protein) in dinosaur bones is convincing. Immunological experiments suggest that Tyrannosaurus collagen is very similar to the collagen of—you guessed it—the chicken.
Advances in understanding the master genes that control fundamental developmental processes, such as where limbs should appear on a vertebrate body, and how many digits they should have, are at the root of the field of evolution and development—evo-devo. This all leads Horner to ask—what if we can inject substances into chicken embryos at just the right place and time to reprogram development so that structures lost in deep time are regenerated in a modern chicken?
There need not be any changes made to the chicken genome—only changes in how the chicken develops, and perhaps the reactivation of some long dormant genes. Working on how to reprogram the stubby chicken tail known as the pygostyle so it develops into the long vertebrate tail of a small dinosaur might be the place to start.
From Dinosaur to Chicken and Back
After the convincing set up, which makes what is to come seem entirely plausible, Horner finally gets down to presenting his principle idea. Since chickens are probably the closest living ancestors to the extinct non-avian dinosaurs (some scientists would go so far as call them dinosaurs in fact), the chicken genome offers the best hope for generating atavistic (evolutionary throwback) structures in a modern organism.
Horner, being an excellent scientist, presents both sides of the argument for why this should (or perhaps should not) be done. He makes the case that it would not be cruel to a chicken to perform such an experiment, and that there is no threat of vicious little carnivores being loosed on the world.
That is really the beauty of such an experiment if it should succeed—and Horner does not pretend it will be easy—no actual genetic changes in the chicken are needed. Thus, if a dinochicken were to escape the lab and somehow mate with a normal chicken, the offspring could be nothing other than normal chickens.
It seems like it might eventually work. Multimillion dollar funding for paleontology projects is hard to come by, but if anyone can rev up enough enthusiasm to make a multidisciplinary dinochicken project a reality, it's probably Jack Horner.
References
Horner, Jack, and Gorman, James. How to Build a Dinosaur. New York, NY: Penguin Group, 2009.
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