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Among living dinosaurs, the cassowary is one of the most fantastic. Photo by Paul IJsendoorn, from Wikipedia.

One of the reasons Jurassic Park was so successful–as a novel and a blockbuster film–is that it presented a plausible way to bring dinosaurs back to life. The idea that viable dinosaur DNA might be retrieved from bloodsucking prehistoric insects seemed like a project that could actually succeed. Even though the actual methodology is hopelessly flawed and would never work, the premise was science-ish enough to let us suspend our disbelief and revel in the return of the dinosaurs.

Nevertheless, Jurassic Park brought up the tantalizing possibility that scientists might one day resurrect a Brachiosaurus, Velociraptor or Triceratops. And every once in a while, rumors arise about someone who might just give the project a try. According to the latest round of internet gossip, Australian billionaire Clive Palmer is hoping to clone a dinosaur for an exotic vacation retreat. Palmer has since denied the rumors, but, for a moment, let’s run with the assumption that someone is going to pour millions of dollars into a dinosaur cloning project. Would it actually work?

As Rob Desalle and David Lindley pointed out in The Science of Jurassic Park and the Lost World, there were a lot of steps that Michael Crichton glossed over in his dinosaur cloning regime. The novelist never explained how scientists overcame issues of genetic contamination, figured out what a complete dinosaur genome should look like and, most important of all, figured out how to actually translate all that DNA into a viable dinosaur embryo. It’s not simply a matter of accumulating DNA pieces until scientists have mapped every gene. A creature’s genetics must be read and interpreted within a biological system that will create an actual living organism. There are innumerable hurdles to any speculative dinosaur cloning project, starting with the effort to actually obtain unaltered dinosaur DNA–something that has never been done, and may never be.

If Palmer, or anyone else, wants to create a dinosaur park, it would be far easier to set up a reserve for living dinosaurs. The cassowary–a flightless, helmeted bird–is sufficiently prehistoric-looking to make it a draw for visitors. True, it’s not a Velociraptor, but a cassowary is most certainly a dinosaur that does pack a mean kick. There are plenty of living dinosaurs that could use a hand through conservation programs, so perhaps it would be better to try to save some avian dinosaurs rather than bring their non-avian cousins back from the dead.

How to Build a Dinosaur by Jack Horner and James Gorman

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.

Figure from research paper about genetic lineage of tetropods

When visitors stroll among the remains of ancient beasts in the dinosaur halls of museums, they often focus on how bizarre they were. With the exception of the more bird-like forms, there is nothing like them alive today: immense sauropods with tails and necks that stretched to the horizon, armor-plated ankylosaurs festooned with spikes, stout ceratopsians ornamented with horns and frills, and gargantuan predatory theropods with banana-sized teeth.

What often goes unnoticed is that we share a deep history with these animals. They are, as spectacular as it may sound, our distant relatives. As reviewed in a new paper in the Annual Review of Ecology, Evolution, and Systematics, about 398 million years ago there was a particular group of fish, the lobed-fined or sarcopterygian fish, the organisms that gave rise to our common ancestor with the dinosaurs. The fish lived in freshwater and had a series of bones in their limbs. These and other factors made them different from fish whose fins were supported by a series of spines or fine rays. Within the sarcopterygians was the ancestor of creatures that would appear at about 385 million years ago, the “fishapods” like Panderichthys and Tiktaalik.

Rather than fins, these fishapods had rudimentary limbs which they used to raise their flat bodies up from the muddy bottom. They were equipped with both gills and lungs, and they were among the first creatures to have necks (in their fish ancestors, the shoulder girdle was attached to the skull, prohibiting flexibility). Despite these adaptations, these creatures were not yet walking on land, but their descendants would. It is difficult to pin down precise ancestor-descendant relationships, but it was this sort of creature that gave rise to the first true “limbed” creatures, the earliest tetrapods, which also had fingers and toes. These were animals like Acanthostega that had an amphibious life at the water’s edge.

Even though limbs had evolved in the water, they allowed early tetrapods to haul out onto land, a place inhabited by plants and invertebrates but no other vertebrates. This did not happen until about 330 million years ago, but when it did, it led to an explosion of diversity. Among the diverse forms was the common ancestor of living reptiles and amphibians as well as mammals and dinosaurs.

Lineages diverged and evolved through time, but our common ancestry can still be seen in our skeletons. We and dinosaurs share body plans based upon four limbs. Although our skeletons have been modified in different ways, we have many of the same types of bones (the bones of our limbs and hands are a good example), and this all goes back to our swamp-dwelling common ancestor almost 400 million years ago.