 The cheek teeth–molars and premolars–were all double-rooted, and the lower molars were serrated and triangular.In the holotype of "M. colliveri", only the second vertebra of the neck–the axis–is preserved.Unlike in modern baleen whales, but similar to archeocetes and the ancient toothed baleen whale "Aetiocetus", the breastbone is composed of several pieces.