With its large auditory bullae and 25cm external ear lobes, the okapi has acute hearing and can hear and transmit low-frequency infrasonic sounds below audible range for humans.
The dolichocephalic skull of the okapi is like those of other paleotragines.
The okapi’s skull shows primitive characteristics for the family, including a large parietal region, short diastema, and large auditory bullae. Large palatine sinuses are also distinctive of the okapi, among giraffids.
A large bony capsule enclosing the middle ear bones, (the auditory bullae,) is common to many forest-dwelling ruminants and is related to an acute sense of hearing. In accord, there are large external ear lobes, 25 centimeters in length from the crown, that are readily flexed.
Both features may be correlated with infrasonic sound reception. In fact, studies in 1992 at the San Diego Zoo and White Oak Conservation Center in Florida have demonstrated that the okapi can hear and transmit low-frequency sounds below audible range for humans.