I was searching for more of the mastodon remains, when I saw what looked like a human skull. I had thought we already had a great discovery after finding the remains of several Pleistocene animals…but finding a human skull was totally amazing for us. All of our efforts… walking through the jungle, carrying all the gear, securing the helium required to do such a deep dive, laying thousands of feet of exploration line… paid off at that moment. This is the Holy Grail of underwater cave exploration," Alex said.