Underdetermination (of the Quine-Duhem sort) makes evolutionary theory per se immune to falsification by the finding of a Precambrian rabbit. Which is more likely: that the rabbit found in what we thought was a Precambrian stratum is actually Precambrian, or that the stratum is not actually Precambrian, or that there was some anomaly that allowed this rabbit (which lived long after the Precambrian era) to become embedded in this Precambrian stratum? A certain view of evolutionary history (or certain proposed phylogenies and taxonomies) might be falsified in this manner, but not evolutionary theory per se.
A case could be made in support of evolutionary theory as an inference to the best explanation, no matter what the fossil record looked like.
-A8