Ancient sperm whales differ from modern sperm whales in tooth count and the shape of the face and jaws. For example, "Scaldicetus" had a tapered rostrum. Genera from the Oligocene and Miocene had teeth in their upper jaws. These anatomical differences suggest that these ancient species may not have necessarily been deep-sea squid hunters like the modern sperm whale, but that some genera mainly ate fish. Contrary to modern sperm whales, most ancient sperm whales were built to hunt whales. "Livyatan" had a short and wide rostrum measuring across, which gave the whale the ability to inflict major damage on large struggling prey, such as other early whales. Species like these are collectively known as killer sperm whales.