The evolution or appearance of whales as been extraordinarily explosive (non-gradual). On the traditional evolutionary model, a coyote-like creature (Pakicetus)1 was transformed into a fully-aquatic whale within 4 million years, (perhaps significantly less) despite the requirements:
New life-forms appear suddenly in the fossil record.1 This is relevant because, unless life were appearing suddenly in life-history, the fossil record would not be this way.
But so what if the fossil record only shows new life-forms arriving suddenly. Couldn't it be that the relevant rocks have been eroded or remain undiscovered (i.e. the appearance is an “artifact” of an incomplete sampling).
Stephen Jay Gould (Professor at Harvard, Paleonotologist): “The extreme rarity of transitional forms in the fossil record persists as the trade secret of paleontology. The evolutionary trees that adorn our textbooks have data only at the tips and nodes of their branches; the rest is inference, however reasonable, not the evidence of fossils. … We fancy ourselves as the only true students of life's history, yet to preserve our favored account of evolution by natural selection we view our data as so bad that we never see the very process we profess to study. For several years, Niles Eldredge of the American Museum of Natural History and I have been advocating a resolution to this uncomfortable paradox.” [“Evolution's Erratic Pace” in Natural History 86(5)(1977): 12-16.]