Evolutionary simplification in the human larynx – the loss of vocal membranes and air sacs common to all nonhuman primates – enabled the increased acoustic complexity required by human speech, ...
Griffiths, Thomas A. 1983. "Comparative laryngeal anatomy of the Big Brown bat, Eptesicus fuscus, and the Mustached bat, Pteronotus parnellii." Mammalia, 47, (3) 377–394.