A friend and I were discussing extinct megafauna not too long ago, and after reading an article on the breathtaking Brontoscorpio he tilted his head slightly and said rather longingly, "I wish they could bring some of these animals back, you know, just so we could see what they were like." Oh how many times people have thought just that over the ages. Although I don't think a person would take encountering an aquatic scorpion roughly the size of a child too well, the sheer idea of witnessing such an animal has captivated the minds of millions. The idea of something like a dinosaur is so incredible, so seemingly intangible that even the fossilized bones of these mammoth creatures seem almost an illusion at the time, as though such a creature could never have existed. I belive part of the main fascination with ressurrecting these great reptiles lies in the fact that we would like to see for ourselves if such creatures are even possible, or if things are like Douglas Adams' The Hitchhiker's Guide to the Galaxy, in which the creators of life just buried the bones beneath the soil simply to intrigue us.
Understandably enough, the idea of cloning a dinosaur in simply maddening in its appeal. With genetic technology, it has seemed even more within our grasp as science has cloned sheep, lizards, and even pets. Recently extinct animals even now can possibly be resurrected. There is that tiny scrap of a chance that a frozen mammoth in Siberia still yields some DNA, or perhaps a shred of thylacine (a.k.a. the Tasmanian wolf, or the Tasmanian tiger) DNA survived its extinction. What wonder it would be, to see and study these long-gone creatures. So many of Earth's mysteries could be revealed, and now more than ever the brink of that scientific nirvana can be seen. Alas, while we may be lucky enough to see an aurochs, we will never see an apatosaurus.
The first and most obvious reason why we cannot clone dinosaurs is the process of fossilization itsself. By definition, fossilization is the process by which all organic material in a dinosaur is replaced by minerals, resulting in rock. Simple, boring rock. A fossil is not by any means the remains of a dinosaur. A fossil is simply a bone-shaped rock, or a feather-shaped rock, or whatever else they may dig up. Dinosaurs have been dead, at the earliest, 65 million years so the very thought of any tissue surviving is unfeasible. Fossils are the ones lucky enough to have been compressed in mud that hardened before the animal was completely rotted away. After millions of years, even bone turns to dust. Anything that could contain DNA, the key to cloning, anything that could have tissue, is gone, rotted, returned to the soil. Truth be told the soil that was nourished by a dead dinosaur probably holds more of the creature's life than the fossil itsself.
In the movie Jurassic Park, cloning is done by extracting the DNA of a mosquito perserved perfectly in amber. Unfortunately, genetics doesn't work like that. The DNA of the mosquito was mixed in a reptile egg to form a dinosaur. This argument is simple enough. Two sets of genes don't mix like that. You have to have dinosaur genes. An artropod is an arthropod and a reptile is a reptile.
Even if cloning were possible, the implications of "What the heck am I going to do to hatch this thing?!" still remain. To clone an animal, the genetic material must be vacuumed out of an egg and replaced with the genetic material of the "host" creature. It's a concept similar to trying to revive a megatherium. A ground sloth that big can't grow inside a common three-toed sloth...or most mammals, for that matter. Finding an enviornment in which the embryo would thrive would be difficult due to the utter uniqueness of dinosaurs. Most common reptiles are too small, and although ostrich eggs would probably work, it would work better for bipedal carnivores, which are genetically related to birds (particularly of the flightless variety). Let's be frank: a T-Rex would be interesting, but do you really, really want one of those things in the local zoo?
However, genetics doesn't fail us completely. While we may not be able to clone our fossil friends, evidence shows that DNA still contains the most ancient codes for life, dating all the way back to lowly blue-green algae. The genetic code has been building and building for eons. If the theory of common descent holds true, then the genetics for a stegosaurus lie somewhere in every animal on earth because the first cell of life mutated into another form of life, and that mutated, and that mutated, and history was made. Genetically speaking, almost all animals have the same basic DNA with nucleotides in different orders. And all animals have Earth's genetic history encoded deep inside them. Extraction and manipulation of these codes could, in theory, re-create something similar to a dinosaur, or a smilodon. It wouldn'd be a clone, for a clone is a genetic double, but it would be something we've never seen before and that is worth a try.
Cloning of dinosaurs will never be a reality simply due to the fact that all we have now are rocks. Genetics may be advanced, but it isn't magical. However, the very tenacity of genes themselves may hold a different way to man's dream of witnessing the "terrible lizards" one last time. Though cloning holds the "sci-fi" intrigue, it is not the road we should look toward if we want to see a dinosaur.