Could we resurrect dinosaurs from fossil embryos?

In the 1994 movie "Dumb and Dumber," Mary Swanson tells Lloyd Christmas that their chances of ending up together are "one out of a million," to which he replies, "So you're telling me there's a chance."

Paleontologists must sometimes feel like Mary when answering questions about dinosaur de-extinction. They must also wonder how so many people could watch "Jurassic Park" and its sequels and miss the persistent theme of unintended consequences.

Does the discovery of dino embryos open up a new avenue to reptilian rebirth? The answer is no. Dinosaur eggs are tens to hundreds of millions of years past their Use By date, and fossilized to boot -- not exactly prime incubator material. As for the embryos, they are just so many piles of bone. Not much help there.

What about the organic material -- have we finally dug up dinosaur DNA? Not exactly. Paleontological circles have been debating possible organic tissue finds for years, but they have yet to find DNA (and likely never will -- see sidebar).

Take the Tyrannosaurus rex, for example. In 2005, scientists using weak acid to demineralize Tyrannosaurus bone pulled soft, pliable "tissues" from the remains, including bits that resembled bone cells, red blood cells and blood vessels. Later finds provided further samples of preserved tissues from a variety of species and time periods, suggesting this discovery was no fluke [sources: Kaye et al.; Schweitzer et al.; Schweitzer et al.].

Needless to say, people got a little excited. In a game of inches like paleontology, such a find amounted to a touchdown, but research referees soon rolled back the scoreboard. Upon further review via carbon dating and scanning electron microscopy, they announced that the stringy bits and hollows were not dinosaur tissues but bacterial biofilms -- collections of bacteria bound together by polysaccharides, proteins and/or DNA. They might look the part, but they actually have more in common with tooth plaque than dinosaur cells [sources: Bayles; Kaye et al.].

Whatever their nature, the finds made paleontologists wonder; Might the real thing be out there, waiting to be discovered? They adjusted their techniques and, with the Lufengosaurus nest, struck pay dirt. Exciting? Absolutely. Organic? Sure. DNA? Not by a long shot [source: Reisz et al.].

But suppose it had been?

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].