Back-breeding and Filling in the Blanks

There's more than one way to skin an extinct saber-tooth cat. Scientists could take fragments of DNA and knit them together with sequences from living cousins, much as avian, amphibian and reptile DNA filled genetic gaps in "Jurassic Park." They could then clone the modified cells [source: Kolata].

Not All It's Cracked Up to Be

Over the past decade, advances in stem cells, salvaging ancient DNA and rebuilding genomes have brought the concept of "de-extinction" -- particularly of genetic cousins of living species -- closer to realization [sources: Kolata; Zimmer]. Just how close, and what this might mean to much more ancient animals, remains less clear.

Using frozen cells, scientists in 2003 successfully cloned an extinct Pyrenean ibex, aka a bucardo (Capra pyrenaica pyrenaica), but it died minutes later [sources: Kolata; Mabry; Zimmer]. For years, Australian researchers have been trying to return the Southern gastric brooding frog (Rheobatrachus silus), the last of which croaked several decades ago, to the lily pad of the living, but the results have yet to last beyond the early embryonic stage [source: Kolata].

Although stumbling, these first steps raise hopes of more ambitious resurrections to come, including woolly mammoths, passenger pigeons and a Yukon horse extinct for around 70 millennia -- which sounds like a long time, until you realize it's only one-tenth of 1 percent as long ago as the most recent dinosaur extinction [source: Kolata].

Even if dino DNA were no older than yesterday's yogurt, however, numerous ethical and practical concerns should cause all but the maddest scientists to hesitate before sending in the clones. After all, how would we regulate such a process? Who would perform it and when? How would de-extinction affect the Endangered Species Act? What of the pain and suffering experienced by failed attempts? Might we breed dead diseases back into existence, or end up with the equivalent of invasive species on steroids [sources: Kolata; Mabry]?

There are upsides, of course. Much like the reintroduction of wolves to Yellowstone Park, "rolling back" recent extinctions could help restore balance to damaged ecosystems, and some say mankind owes a debt to the animals it has offed [sources: Kolata; Mabry; Zimmer].

For now at least, the DNA issue makes the question academic. It is conceivable that a much more recent creature, such as a frozen woolly mammoth, might produce an intact (if freezer-burned) cell, but as far as dinosaurs are concerned, Lufengosaurus' broken-down proteins might be the closest we ever come to "Jurassic Park" [source: Kolata].

Alternatively, they could try to "back-breed" an ancestral animal into existence by mating descendants with distinctive genes inherited from it. Since 1945, some German breeders have claimed to have accomplished the feat with the aurochs (Bos primigenius), an extinct wild ox and progenitor of modern cattle, but scientists remain dubious [sources: Encyclopaedia Britannica; Kolata].