However, both groups began with generalized basal ungulate-type cheek teeth adapted for eating soft plant foods, and readapted them for a carnivorous diet; they are the only known mammal groups to have done this. Other characters Sinonyx'' has in common with early whales include an ossified tympanic bulla, which improves sensitivity to high-frequency sounds and is often seen in predators that hunt small prey by sound, and an enlarged jugular foramen, which gives more room for the cranial nerves that control swallowing and the balance between athletic activity and digestion.
This is because both groups initially had generalized basal ungulate-type cheek teeth adapted for eating soft plant foods, but later modified them to accommodate a carnivorous diet; they are the sole known mammal groups to have accomplished this. Other characteristics of Sinonyx that are similar to early whales include an ossified tympanic bulla and an enlarged jugular foramen.