Megalodon, the largest shark that ever lived, is known only from its gigantic bladelike teeth, which can be more than 7 inches long. But these teeth, described by some scientists as the "ultimate cutting tools, " took millions of years to evolve into their final, iconic form. Megalodon's earliest ancestor, Otodus obliquus, sported three-pronged teeth that could have acted like a fork for grasping and tearing fast-moving fishes. In later megatooth shark species, teeth flattened and developed serrated edges, transitioning to a knifelike shape for killing and eating fleshy animals like whales and dolphins. But the final tooth evolution in this lineage of powerful predators still took 12 million years, a new study shows. An analysis of teeth from megalodon and its immediate ancestor, Carcharocles chubutensis, traced the unusually slow, gradual shift from a large tooth flanked by mini-teeth -- known as lateral cusplets -- to teeth without these structures.
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