Evolutionary biologist Richard Dawkins said that the discovery of fossil mammals in Precambrian rocks would "completely blow evolution out of the water." Philosopher Peter Godfrey-Smity doubted that a single set of anachronistic fossils, however, even rabbits in the Precambrian, would disprove the theory of evolution outright. The first question raised by the assertion of such a discovery would be whether the alleged "Precambrian rabbits" really were fossilized rabbits. Alternative interpretations might include incorrect identification of the "fossils", incorrect dating of the rocks, and a hoax such as the Piltdown Man was shown to be.
Even if the "Precambrian rabbits" turned out to be genuine, they would not instantly refute the theory of evolution, because that theory is a large package of ideas, including: that life on Earth has evolved over billions of years; that this evolution is driven by certain mechanisms; and that these mechanisms have produced a specific "family tree" that defines the relationships among species and the order in which they appeared. Hence, "Precambrian rabbits" would prove that there were one or more serious errors somewhere in this package, and the next task would be to identify the error(s).
http://en.wikipedia.org/wiki/Precambrian_rabbit#cite_note-GodfreySmith2003TheoryAndReality-1
Benton pointed out that, in the short term, scientists often have to accept the existence of competing hypotheses, each of which explains large partsbut not allof the observed relevant data.