Mammalodontidae

• the mandibular symphysis is short, has a rugose joint surface, but lacks a symphyseal groove. In archaeocetes the symphysis is long. In modern mysticetes, in contrast, the symphysis is very small, its joint surfaces are smooth, and there is a groove on the interior side of the mandible that accommodates the symphyseal ligament which enables them to open their mouth wide.
• the external foramina on the mandible are relatively large
• the postcanines sit in a longitudinal groove flanked by a lateral edge
• the alveolar margin forms an angle with the ventral margin
• the ventral margin is straight in the posterior half of the mandible
• teeth have longitudinal ridges
• posterior postcanines have two roots joined below the crown base
• postcanines are densely packed without long diastemata