When the film adaptation of the science fiction novel Jurassic Park premiered in the summer of 1993, scientists and the public alike wondered if it was possible to bring dinosaurs back from the dead. It was a tantalizing prospect, but the general consensus was that even if dinosaur DNA could be recovered, there were simply too many obstacles. Cloning a non-avian dinosaur appeared to be all but impossible.
Yet perhaps there was another way. In the 1993 NOVA program "The Real Jurassic Park," paleontologist Robert Bakker suggested that since birds were living dinosaurs, they still carried the genetic code for the formation of teeth, a long tail, and other "dinosaurian" features. If these genetic "switches" could be turned back on then scientists could, to a limited extent, reverse-engineer a dinosaur. Sixteen years later paleontologist Jack Horner has further developed this hypothesis and, with science writer James Gorman, explained it in his new book How to Build a Dinosaur.
When I hear the word "paleontologist" I almost always think of a flannel-clad scientist prying an ancient monster from the rock of a dusty and barren landscape. To some extent this association is accurate, but during the past few decades the discipline of paleontology has diversified to include researchers who specialize in microbiology, development, and genetics. From the structure of dinosaur bone to the controversy over potential Tyrannosaurus rex soft tissue, the first half of the book focuses on how paleontology has been married to laboratory biology. While readers may be itching to get to Horner's recipe for a dinosaur, this section is important. It summarizes the emergence of new areas of study within paleontology and confirms that it is unlikely that we will ever clone a dinosaur from preserved tissue. Dinosaurs, as they were from about 230 to 65 million years ago, are lost forever. Only bones and other rare traces of their existence remain.
This does not seem like a promising start for a book that claiming to explain how to build a dinosaur, but once the changing nature of paleontology is established, Horner & Gorman set off on another route. The science of evolutionary developmental biology, or evo-devo for short, can provide significant clues about major evolutionary changes. This is because evolution is constantly adapting existing structures to new functions. During the evolution of birds, for instance, dinosaurs did not lose their arms only to evolve wings from nothing. Instead the dinosaur forelimb, already feather-clad, was modified for flight.
It is also true that genes, particularly regulatory genes that organize the formation of the body during development, can be preserved and put to new functions just as parts of skeletal anatomy can. This means that by studying the embryological development of living birds, scientists can find clues as to how the bodies of some dinosaurs were formed. By tweaking the development of a chicken embryo they might be able to create a creature with a long tail, clawed hands, and teeth, just as Bakker suggested in 1993. The precise details of how this could be done are still largely unknown, Horner has no "recipe" to share, but the hypothesis that it could be done has merit.
(Wired magazine has an interview with Horner in which he proposes that by switching certain genes on or off during the development of a chicken, you could create something that looked more like Velociraptor and less like something destined to be made into deep fried nuggets.)
If these experiment were successful, the resulting creature would not be a true dinosaur; it would simply be a genetically manipulated chicken that would appear dinosaur-like. It would mostly be informative about the small maniraptoran dinosaurs from which birds evolved and would be less informative for the sauropods and the vast array of ornithischian dinosaurs (hadrosaurs, stegosaurs, ceratopsians, etc.). Horner & Gorman readily recognize this, and it is just as well. The goal of the project is not to create a living dinosaur but to understand how evolution works. If a creature could be created that revealed how the genetic code for ancient characteristics has been retained and re-activated, the animal would be a striking illustration of evolution. More than that, by bringing these traits out paleontologists may be able to understand the details of how birds evolved from theropod dinosaurs.
The importance of How to Build a Dinosaur does not lie in Horner's wish to create a dinochicken. That makes up only a small part of the book. Instead the slim volume indicates how paleontology is becoming more of an interdisciplinary science where studies of development and genetics are just as important as fossilized bones. It remains to be seen whether Horner will be able to open a "Jurassic Barnyard", but that is not the point. The bodies of living things hold records of the past just as the strata of the earth do, and when both lines of evidence are studied together scientists can finally begin to answer evolutionary questions that have puzzled researchers for decades.