Jaws

Jaws apparently weren't an instant hit in the world's oceans.  New research published in Nature shows that it was almost 30 million years after the appearance of the first jawed vertebrates before they were able to make a serious dent in the success of previously dominant jawless fish.  Also worth noting that there was no detectable niche shift on the the part of the developing jawed fishes to fill the niches vacated by their declining counterparts.