Researchers speculate that 2 to 8 new cetacean species and almost 10 marine reptile species (like sea snakes) remain to be discovered.

UNESCO: THEMES

"Snakes will rarely strike a flagging adult squirrel, and if they do they almost always miss, " said Rulon Clark, assistant professor of biology at San Diego State University.

CNN: April 4, 2012 -- Updated 1350 GMT (2150 HKT)

What at first glance appears to be a jumble of boulders was probably a workshop where expert stonecutters practiced their trade. (One chunk of granite has been carved into almost-finished steps.) Another large stone, known as Serpent Rock, has snakes etched into its top surface.

BBC: What most people miss at Machu Picchu