Unlike the modern sperm whale which has teeth in its lower jaw only, Brygmophyseter has 12 functional teeth on each side of the lower jaws and 12 functional teeth on each side of the upper jaws.A nearly complete fossil specimen of this ancient whale from Japan is about 7 meters (23 feet) long. However, some paleontologists had estimated that Brygmophyseter could had potentially grown up to 12 meters (40 feet) long.
It may have employed sonar to track and disorient a prey item in deep waters, like the modern age sperm whales. It may also have used its large head to ram a potential opponent during conflict. Brygmophyseter would also have lived in social groups called pods, and probably hunted in packs, like modern age orcas.
Brygmophyseter likely preyed upon a variety of animals including fish, pinnipeds,giant squid and cetaceans.