Once inside the cave, Milo proceeds to show Cornelius one of his precious artifacts - the bones of a hitherto undiscovered animal species. Meanwhile, Zira is doing some excavating of her own - and stumbles across a fossil so unusual and significant it could shake the foundations of Ape society's whole belief system...
The skull of a human - wearing spectacles! This proves that humans, presently mute, imbecile beasts, once possessed a technology far in advance of that of the apes.
"Come on, Zira. We'll go and pick up my dating equipment,
then we'll be able to find out how old that skull is."