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.
On the other hand, both groups initially had generalized basal ungulate-type cheek teeth adapted for eating soft plant foods, but later evolved them to suit a carnivorous diet; they are the only known mammal groups to have undergone this transformation. Other characteristics of Sinonyx that are similar to early whales include an ossified tympanic bulla, which improves hearing in high-frequency sounds, and an enlarged jugular foramen, which allows for better control over swallowing and balance between physical exertion and digestion.