Those hand prints on cave walls? Lizard hands.

Not all hand silhouettes - but apparently some of these...

Wadi Sura II is considered one of the greatest rock art sites of the Sahara, although it lacks the popular fame of nearby Wadi Sura I, the "Cave of the Swimmers," which was discovered by Hungarian count Láslo Almásy in 1933 and popularized in "The English Patient."...

Anthropologist Emmanuelle Honoré of the McDonald Institute for Archaeological Research describes how she was "shocked" by the shape of the unusually small hand outlines when she saw them at her first visit to Wadi Sura II in 2006. "They were much smaller than human baby hands, and the fingers were too long," she explains....

 Honoré initially suspected monkey paws, but when those proportions were also off, colleagues at the Museum of Natural History in Paris suggested she take a look at reptiles. So far, the examples that have proportions closest to the "baby" hands come from the forelegs of desert monitor lizards or, possibly, the feet of young crocodiles. (The crocodile study is still in progress.) Monitor lizards still live in the region today and are considered protective creatures by nomadic tribes in the area.  

The revelation that the small hand images from Wadi Sura II are not even human is a big surprise for researchers who study Saharan rock art. "Animal stenciling is mostly considered an Australian or South American thing," Honoré explains.   

The story continues at National Geographic, via Smithsonian.