Huge headed Skulls found in Mexico, possibly not of this World

These skulls were photographed by Robert Connolly on his trip around the world during which he was collecting materials about ancient civilizations. The discovery of unusual skulls was thus an unintended "spinoff" of his efforts.

In most respects it appears to be that of a human, except that it has an extraordinarily large cranium and eye sockets. The eye sockets are about 15 percent larger than a modern human's. The age and date of the skull are unknown. Similar skulls appear in remains found in a Mexican cave. Could they all be genetic mutations, some unknown species of creature or something not of this world?