In both remingtonocetids and protocetids, the size of mandibular foramen had increased.

The large mandibular foramen indicates that the mandibular fat pad was present.

The medial surface presents about its center the oblique mandibular foramen, for the entrance of the inferior alveolar vessels and nerve.

Mandibular foramen, paired, in the inner (medial) aspect of the mandible, superior to the mandibular angle in the middle of the ramus.

The jawbone of pakicetids also lacks the enlarged space (mandibular foramen) that is filled with fat or oil, which is used in receiving underwater sound in modern whales.

The fat pad passes anteriorly into the greatly enlarged mandibular foramen to reach in under the teeth, and posteriorly to reach the thin lateral wall of the ectotympanic.

Plain 'ol archosaurs (including both crocs and dinos) are diagnosed by: , antorbital fenestra in snout wall between nostril and orbit, laterally flattned teeth with serrations, ossified laterosphenoid in braincase, lateral mandibular foramen in posterior lower jaw bones.