Handout of divers Nava and Bird transporting a skull to an underwater turntable for photographing in an underwater cave in Mexico’s Yucatan Peninsula

Divers Alberto Nava and Susan Bird transport a skull to an underwater turntable so that it can be photographed in order to create a 3-D model at the bottom of the underwater cave on Mexico’s Yucatan Peninsula June 15, 2013 in this handout photo provided by National Geographic May 15, 2014. REUTERS/Paul Nicklen/National Geographic/Handout via Reuters